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 $60.88   11.277%   $67.7454   $67.75   $67.75   $67.70  
  Purchase #2 $15.80   6.314%   $16.7976   $16.80   $16.80   $16.80  
  Purchase #3 $186.71   6.728%   $199.2718   $199.27   $199.25   $199.30  
  Purchase #4 $238.41   12.174%   $267.434   $267.43   $267.45   $267.40  
  Purchase #5 $101.46   7.854%   $109.4287   $109.43   $109.45   $109.40  
  Purchase #6 $8.65   6.144%   $9.1815   $9.18   $9.20   $9.20  
  Purchase #7 $247.26   10.311%   $272.755   $272.76   $272.75   $272.80  
  7 purchase totals = $859.17       $942.6140   $942.62   $942.65   $942.60