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 $85.68   12.819%   $96.6633   $96.66   $96.65   $96.70  
  Purchase #2 $48.82   3.644%   $50.599   $50.60   $50.60   $50.60  
  Purchase #3 $206.57   8.228%   $223.5666   $223.57   $223.55   $223.60  
  Purchase #4 $195.29   8.805%   $212.4853   $212.49   $212.50   $212.50  
  Purchase #5 $136.58   8.516%   $148.2112   $148.21   $148.20   $148.20  
  Purchase #6 $22.79   11.220%   $25.347   $25.35   $25.35   $25.30  
  Purchase #7 $72.39   3.679%   $75.0532   $75.05   $75.05   $75.10  
  7 purchase totals = $768.12       $831.9256   $831.93   $831.90   $832.00