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 $86.87   6.490%   $92.5079   $92.51   $92.50   $92.50  
  Purchase #2 $155.53   8.682%   $169.0331   $169.03   $169.05   $169.00  
  Purchase #3 $135.92   9.541%   $148.8881   $148.89   $148.90   $148.90  
  Purchase #4 $211.96   4.115%   $220.6822   $220.68   $220.70   $220.70  
  Purchase #5 $61.81   8.139%   $66.8407   $66.84   $66.85   $66.80  
  Purchase #6 $138.57   10.358%   $152.9231   $152.92   $152.90   $152.90  
  Purchase #7 $199.61   13.135%   $225.8288   $225.83   $225.85   $225.80  
  7 purchase totals = $990.27       $1,076.7039   $1,076.70   $1,076.75   $1,076.60