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 $67.99   13.203%   $76.9667   $76.97   $76.95   $77.00  
  Purchase #2 $130.58   12.317%   $146.6635   $146.66   $146.65   $146.70  
  Purchase #3 $24.47   10.263%   $26.9814   $26.98   $27.00   $27.00  
  Purchase #4 $136.44   13.644%   $155.0559   $155.06   $155.05   $155.10  
  Purchase #5 $163.29   12.290%   $183.3583   $183.36   $183.35   $183.40  
  Purchase #6 $148.85   4.650%   $155.7715   $155.77   $155.75   $155.80  
  Purchase #7 $190.53   12.443%   $214.2376   $214.24   $214.25   $214.20  
  7 purchase totals = $862.15       $959.0349   $959.04   $959.00   $959.20