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 $205.70   13.127%   $232.7022   $232.70   $232.70   $232.70  
  Purchase #2 $229.29   9.434%   $250.9212   $250.92   $250.90   $250.90  
  Purchase #3 $125.25   9.387%   $137.0072   $137.01   $137.00   $137.00  
  Purchase #4 $59.60   7.477%   $64.0563   $64.06   $64.05   $64.10  
  Purchase #5 $62.65   10.586%   $69.2821   $69.28   $69.30   $69.30  
  Purchase #6 $189.28   12.568%   $213.0687   $213.07   $213.05   $213.10  
  Purchase #7 $8.44   13.462%   $9.5762   $9.58   $9.60   $9.60  
  7 purchase totals = $880.21       $976.6139   $976.62   $976.60   $976.70