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 $228.84   11.735%   $255.6944   $255.69   $255.70   $255.70  
  Purchase #2 $93.67   9.262%   $102.3457   $102.35   $102.35   $102.30  
  Purchase #3 $196.89   13.679%   $223.8226   $223.82   $223.80   $223.80  
  Purchase #4 $110.95   9.394%   $121.3726   $121.37   $121.35   $121.40  
  Purchase #5 $47.39   12.326%   $53.2313   $53.23   $53.25   $53.20  
  Purchase #6 $12.34   13.140%   $13.9615   $13.96   $13.95   $14.00  
  Purchase #7 $14.59   11.279%   $16.2356   $16.24   $16.25   $16.20  
  7 purchase totals = $704.67       $786.6637   $786.66   $786.65   $786.60