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 $7.25   9.801%   $7.9606   $7.96   $7.95   $8.00  
  Purchase #2 $232.61   5.662%   $245.7804   $245.78   $245.80   $245.80  
  Purchase #3 $59.34   5.376%   $62.5301   $62.53   $62.55   $62.50  
  Purchase #4 $117.61   13.560%   $133.5579   $133.56   $133.55   $133.60  
  Purchase #5 $6.84   6.200%   $7.2641   $7.26   $7.25   $7.30  
  Purchase #6 $112.99   8.133%   $122.1795   $122.18   $122.20   $122.20  
  Purchase #7 $29.42   8.827%   $32.0169   $32.02   $32.00   $32.00  
  7 purchase totals = $566.06       $611.2895   $611.29   $611.30   $611.40