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 $203.82   11.856%   $227.9849   $227.98   $228.00   $228.00  
  Purchase #2 $236.29   9.869%   $259.6095   $259.61   $259.60   $259.60  
  Purchase #3 $94.68   4.464%   $98.9065   $98.91   $98.90   $98.90  
  Purchase #4 $198.47   3.765%   $205.9424   $205.94   $205.95   $205.90  
  Purchase #5 $220.84   5.216%   $232.359   $232.36   $232.35   $232.40  
  Purchase #6 $106.43   3.604%   $110.2657   $110.27   $110.25   $110.30  
  Purchase #7 $121.30   3.472%   $125.5115   $125.51   $125.50   $125.50  
  7 purchase totals = $1,181.83       $1,260.5795   $1,260.58   $1,260.55   $1,260.60