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 $59.97   5.659%   $63.3637   $63.36   $63.35   $63.40  
  Purchase #2 $76.55   6.172%   $81.2747   $81.27   $81.25   $81.30  
  Purchase #3 $195.35   11.463%   $217.743   $217.74   $217.75   $217.70  
  Purchase #4 $74.74   5.270%   $78.6788   $78.68   $78.70   $78.70  
  Purchase #5 $137.83   5.411%   $145.288   $145.29   $145.30   $145.30  
  Purchase #6 $11.54   12.403%   $12.9713   $12.97   $12.95   $13.00  
  Purchase #7 $162.61   5.607%   $171.7275   $171.73   $171.75   $171.70  
  7 purchase totals = $718.59       $771.0470   $771.04   $771.05   $771.10