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 $111.95   6.313%   $119.0174   $119.02   $119.00   $119.00  
  Purchase #2 $145.53   8.738%   $158.2464   $158.25   $158.25   $158.20  
  Purchase #3 $82.60   8.730%   $89.811   $89.81   $89.80   $89.80  
  Purchase #4 $77.35   13.426%   $87.735   $87.74   $87.75   $87.70  
  Purchase #5 $203.73   12.874%   $229.9582   $229.96   $229.95   $230.00  
  Purchase #6 $21.65   5.587%   $22.8596   $22.86   $22.85   $22.90  
  Purchase #7 $222.66   13.721%   $253.2112   $253.21   $253.20   $253.20  
  7 purchase totals = $865.47       $960.8388   $960.85   $960.80   $960.80