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 $177.58   13.196%   $201.0135   $201.01   $201.00   $201.00  
  Purchase #2 $52.99   5.146%   $55.7169   $55.72   $55.70   $55.70  
  Purchase #3 $58.69   12.541%   $66.0503   $66.05   $66.05   $66.10  
  Purchase #4 $214.98   4.199%   $224.007   $224.01   $224.00   $224.00  
  Purchase #5 $143.45   11.174%   $159.4791   $159.48   $159.50   $159.50  
  Purchase #6 $136.87   10.394%   $151.0963   $151.10   $151.10   $151.10  
  Purchase #7 $58.36   12.135%   $65.442   $65.44   $65.45   $65.40  
  7 purchase totals = $842.92       $922.8051   $922.81   $922.80   $922.80