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 $184.76   12.809%   $208.4259   $208.43   $208.45   $208.40  
  Purchase #2 $45.48   6.774%   $48.5608   $48.56   $48.55   $48.60  
  Purchase #3 $208.92   13.497%   $237.1179   $237.12   $237.10   $237.10  
  Purchase #4 $95.63   6.112%   $101.4749   $101.47   $101.45   $101.50  
  Purchase #5 $232.33   11.779%   $259.6962   $259.70   $259.70   $259.70  
  Purchase #6 $116.78   7.297%   $125.3014   $125.30   $125.30   $125.30  
  Purchase #7 $188.61   6.860%   $201.5486   $201.55   $201.55   $201.50  
  7 purchase totals = $1,072.51       $1,182.1257   $1,182.13   $1,182.10   $1,182.10