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 $186.92   8.250%   $202.3409   $202.34   $202.35   $202.30  
  Purchase #2 $134.87   5.513%   $142.3054   $142.31   $142.30   $142.30  
  Purchase #3 $56.63   4.741%   $59.3148   $59.31   $59.30   $59.30  
  Purchase #4 $211.89   11.206%   $235.6344   $235.63   $235.65   $235.60  
  Purchase #5 $104.62   5.382%   $110.2506   $110.25   $110.25   $110.30  
  Purchase #6 $31.57   3.294%   $32.6099   $32.61   $32.60   $32.60  
  Purchase #7 $62.53   10.753%   $69.2539   $69.25   $69.25   $69.30  
  7 purchase totals = $789.03       $851.7099   $851.70   $851.70   $851.70