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 $225.52   9.611%   $247.1947   $247.19   $247.20   $247.20  
  Purchase #2 $118.86   6.430%   $126.5027   $126.50   $126.50   $126.50  
  Purchase #3 $140.26   6.653%   $149.5915   $149.59   $149.60   $149.60  
  Purchase #4 $214.61   8.152%   $232.105   $232.11   $232.10   $232.10  
  Purchase #5 $215.94   5.462%   $227.7346   $227.73   $227.75   $227.70  
  Purchase #6 $235.96   13.759%   $268.4257   $268.43   $268.45   $268.40  
  Purchase #7 $180.40   11.857%   $201.79   $201.79   $201.80   $201.80  
  7 purchase totals = $1,331.55       $1,453.3442   $1,453.34   $1,453.40   $1,453.30