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 $243.73   9.673%   $267.306   $267.31   $267.30   $267.30  
  Purchase #2 $80.90   3.703%   $83.8957   $83.90   $83.90   $83.90  
  Purchase #3 $234.73   9.786%   $257.7007   $257.70   $257.70   $257.70  
  Purchase #4 $86.57   11.123%   $96.1992   $96.20   $96.20   $96.20  
  Purchase #5 $219.71   3.753%   $227.9557   $227.96   $227.95   $228.00  
  Purchase #6 $91.88   11.668%   $102.6006   $102.60   $102.60   $102.60  
  Purchase #7 $228.94   3.105%   $236.0486   $236.05   $236.05   $236.00  
  7 purchase totals = $1,186.46       $1,271.7065   $1,271.72   $1,271.70   $1,271.70