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 $106.84   9.282%   $116.7569   $116.76   $116.75   $116.80  
  Purchase #2 $15.52   8.607%   $16.8558   $16.86   $16.85   $16.90  
  Purchase #3 $136.71   7.770%   $147.3324   $147.33   $147.35   $147.30  
  Purchase #4 $195.44   4.593%   $204.4166   $204.42   $204.40   $204.40  
  Purchase #5 $219.76   5.562%   $231.9831   $231.98   $232.00   $232.00  
  Purchase #6 $124.64   13.584%   $141.5711   $141.57   $141.55   $141.60  
  Purchase #7 $183.69   11.480%   $204.7776   $204.78   $204.80   $204.80  
  7 purchase totals = $982.60       $1,063.6935   $1,063.70   $1,063.70   $1,063.80