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 $240.77   4.326%   $251.1857   $251.19   $251.20   $251.20  
  Purchase #2 $236.52   9.352%   $258.6394   $258.64   $258.65   $258.60  
  Purchase #3 $162.73   12.302%   $182.749   $182.75   $182.75   $182.70  
  Purchase #4 $66.90   10.117%   $73.6683   $73.67   $73.65   $73.70  
  Purchase #5 $163.54   3.312%   $168.9564   $168.96   $168.95   $169.00  
  Purchase #6 $75.98   6.335%   $80.7933   $80.79   $80.80   $80.80  
  Purchase #7 $74.82   11.391%   $83.3427   $83.34   $83.35   $83.30  
  7 purchase totals = $1,021.26       $1,099.3348   $1,099.34   $1,099.35   $1,099.30