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 $43.42   9.440%   $47.5188   $47.52   $47.50   $47.50  
  Purchase #2 $222.84   11.168%   $247.7268   $247.73   $247.75   $247.70  
  Purchase #3 $123.47   5.263%   $129.9682   $129.97   $129.95   $130.00  
  Purchase #4 $85.81   7.293%   $92.0681   $92.07   $92.05   $92.10  
  Purchase #5 $165.46   10.401%   $182.6695   $182.67   $182.65   $182.70  
  Purchase #6 $167.57   12.594%   $188.6738   $188.67   $188.65   $188.70  
  Purchase #7 $57.62   12.470%   $64.8052   $64.81   $64.80   $64.80  
  7 purchase totals = $866.19       $953.4304   $953.44   $953.35   $953.50