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 $193.57   5.374%   $203.9725   $203.97   $203.95   $204.00  
  Purchase #2 $51.92   13.107%   $58.7252   $58.73   $58.75   $58.70  
  Purchase #3 $30.54   13.335%   $34.6125   $34.61   $34.60   $34.60  
  Purchase #4 $230.51   13.780%   $262.2743   $262.27   $262.25   $262.30  
  Purchase #5 $54.71   5.535%   $57.7382   $57.74   $57.75   $57.70  
  Purchase #6 $250.92   3.214%   $258.9846   $258.98   $259.00   $259.00  
  Purchase #7 $68.53   12.630%   $77.1853   $77.19   $77.20   $77.20  
  7 purchase totals = $880.70       $953.4926   $953.49   $953.50   $953.50