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 $207.94   4.686%   $217.6841   $217.68   $217.70   $217.70  
  Purchase #2 $150.77   11.443%   $168.0226   $168.02   $168.00   $168.00  
  Purchase #3 $149.89   12.376%   $168.4404   $168.44   $168.45   $168.40  
  Purchase #4 $59.58   7.318%   $63.9401   $63.94   $63.95   $63.90  
  Purchase #5 $85.41   11.376%   $95.1262   $95.13   $95.15   $95.10  
  Purchase #6 $198.37   3.241%   $204.7992   $204.80   $204.80   $204.80  
  Purchase #7 $49.73   10.483%   $54.9432   $54.94   $54.95   $54.90  
  7 purchase totals = $901.69       $972.9558   $972.95   $973.00   $972.80