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 $89.56   6.323%   $95.2229   $95.22   $95.20   $95.20  
  Purchase #2 $77.93   5.626%   $82.3143   $82.31   $82.30   $82.30  
  Purchase #3 $209.96   9.618%   $230.154   $230.15   $230.15   $230.20  
  Purchase #4 $210.58   8.304%   $228.0666   $228.07   $228.05   $228.10  
  Purchase #5 $45.43   13.179%   $51.4172   $51.42   $51.40   $51.40  
  Purchase #6 $193.87   6.114%   $205.7232   $205.72   $205.70   $205.70  
  Purchase #7 $55.84   9.715%   $61.2649   $61.26   $61.25   $61.30  
  7 purchase totals = $883.17       $954.1631   $954.15   $954.05   $954.20