Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.86   10.422%   $117.9969   $118.00   $118.00   $118.00  
  Purchase #2 $166.59   13.767%   $189.5244   $189.52   $189.50   $189.50  
  Purchase #3 $200.43   8.753%   $217.9736   $217.97   $217.95   $218.00  
  Purchase #4 $229.57   5.671%   $242.5889   $242.59   $242.60   $242.60  
  Purchase #5 $238.52   7.272%   $255.8652   $255.87   $255.85   $255.90  
  Purchase #6 $241.65   11.486%   $269.4059   $269.41   $269.40   $269.40  
  Purchase #7 $179.84   7.635%   $193.5708   $193.57   $193.55   $193.60  
  7 purchase totals = $1,363.46       $1,486.9257   $1,486.93   $1,486.85   $1,487.00