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 $87.93   9.275%   $96.0855   $96.09   $96.10   $96.10  
  Purchase #2 $139.88   11.185%   $155.5256   $155.53   $155.55   $155.50  
  Purchase #3 $184.97   6.460%   $196.9191   $196.92   $196.90   $196.90  
  Purchase #4 $83.95   12.650%   $94.5697   $94.57   $94.55   $94.60  
  Purchase #5 $145.66   11.111%   $161.8443   $161.84   $161.85   $161.80  
  Purchase #6 $62.51   10.864%   $69.3011   $69.30   $69.30   $69.30  
  Purchase #7 $35.34   3.111%   $36.4394   $36.44   $36.45   $36.40  
  7 purchase totals = $740.24       $810.6847   $810.69   $810.70   $810.60