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 $224.68   10.464%   $248.1905   $248.19   $248.20   $248.20  
  Purchase #2 $53.64   10.330%   $59.181   $59.18   $59.20   $59.20  
  Purchase #3 $153.74   10.716%   $170.2148   $170.21   $170.20   $170.20  
  Purchase #4 $186.60   12.205%   $209.3745   $209.37   $209.35   $209.40  
  Purchase #5 $236.69   13.324%   $268.2266   $268.23   $268.25   $268.20  
  Purchase #6 $216.73   8.787%   $235.7741   $235.77   $235.75   $235.80  
  Purchase #7 $238.69   7.485%   $256.5559   $256.56   $256.55   $256.60  
  7 purchase totals = $1,310.77       $1,447.5174   $1,447.51   $1,447.50   $1,447.60