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 $189.89   6.158%   $201.5834   $201.58   $201.60   $201.60  
  Purchase #2 $53.42   11.192%   $59.3988   $59.40   $59.40   $59.40  
  Purchase #3 $150.69   3.264%   $155.6085   $155.61   $155.60   $155.60  
  Purchase #4 $118.73   5.620%   $125.4026   $125.40   $125.40   $125.40  
  Purchase #5 $159.63   12.766%   $180.0084   $180.01   $180.00   $180.00  
  Purchase #6 $247.34   10.713%   $273.8375   $273.84   $273.85   $273.80  
  Purchase #7 $43.87   13.324%   $49.7152   $49.72   $49.70   $49.70  
  7 purchase totals = $963.57       $1,045.5544   $1,045.56   $1,045.55   $1,045.50