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 $146.57   8.690%   $159.3069   $159.31   $159.30   $159.30  
  Purchase #2 $93.63   3.353%   $96.7694   $96.77   $96.75   $96.80  
  Purchase #3 $207.64   6.792%   $221.7429   $221.74   $221.75   $221.70  
  Purchase #4 $120.87   13.180%   $136.8007   $136.80   $136.80   $136.80  
  Purchase #5 $60.45   12.732%   $68.1465   $68.15   $68.15   $68.10  
  Purchase #6 $155.80   13.811%   $177.3175   $177.32   $177.30   $177.30  
  Purchase #7 $94.62   5.692%   $100.0058   $100.01   $100.00   $100.00  
  7 purchase totals = $879.58       $960.0897   $960.10   $960.05   $960.00