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 $70.97   4.751%   $74.3418   $74.34   $74.35   $74.30  
  Purchase #2 $120.31   11.421%   $134.0506   $134.05   $134.05   $134.10  
  Purchase #3 $176.40   7.287%   $189.2543   $189.25   $189.25   $189.30  
  Purchase #4 $58.77   9.533%   $64.3725   $64.37   $64.35   $64.40  
  Purchase #5 $230.99   12.745%   $260.4297   $260.43   $260.45   $260.40  
  Purchase #6 $209.68   7.720%   $225.8673   $225.87   $225.85   $225.90  
  Purchase #7 $31.64   5.246%   $33.2998   $33.30   $33.30   $33.30  
  7 purchase totals = $898.76       $981.6160   $981.61   $981.60   $981.70