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 $77.85   11.156%   $86.5349   $86.53   $86.55   $86.50  
  Purchase #2 $56.68   10.496%   $62.6291   $62.63   $62.65   $62.60  
  Purchase #3 $220.74   8.177%   $238.7899   $238.79   $238.80   $238.80  
  Purchase #4 $25.26   9.149%   $27.571   $27.57   $27.55   $27.60  
  Purchase #5 $190.88   11.300%   $212.4494   $212.45   $212.45   $212.40  
  Purchase #6 $127.44   9.459%   $139.4945   $139.49   $139.50   $139.50  
  Purchase #7 $182.76   7.165%   $195.8548   $195.85   $195.85   $195.90  
  7 purchase totals = $881.61       $963.3236   $963.31   $963.35   $963.30