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 $228.39   11.560%   $254.7919   $254.79   $254.80   $254.80  
  Purchase #2 $209.94   9.142%   $229.1327   $229.13   $229.15   $229.10  
  Purchase #3 $127.86   4.677%   $133.84   $133.84   $133.85   $133.80  
  Purchase #4 $199.63   4.150%   $207.9146   $207.91   $207.90   $207.90  
  Purchase #5 $91.36   4.741%   $95.6914   $95.69   $95.70   $95.70  
  Purchase #6 $46.91   3.749%   $48.6687   $48.67   $48.65   $48.70  
  Purchase #7 $215.88   11.567%   $240.8508   $240.85   $240.85   $240.90  
  7 purchase totals = $1,119.97       $1,210.8901   $1,210.88   $1,210.90   $1,210.90