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 $56.63   13.372%   $64.2026   $64.20   $64.20   $64.20  
  Purchase #2 $178.76   5.308%   $188.2486   $188.25   $188.25   $188.20  
  Purchase #3 $248.28   4.281%   $258.9089   $258.91   $258.90   $258.90  
  Purchase #4 $229.68   11.452%   $255.983   $255.98   $256.00   $256.00  
  Purchase #5 $167.96   8.244%   $181.8066   $181.81   $181.80   $181.80  
  Purchase #6 $61.30   8.352%   $66.4198   $66.42   $66.40   $66.40  
  Purchase #7 $189.52   13.841%   $215.7515   $215.75   $215.75   $215.80  
  7 purchase totals = $1,132.13       $1,231.3210   $1,231.32   $1,231.30   $1,231.30