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 $62.31   8.741%   $67.7565   $67.76   $67.75   $67.80  
  Purchase #2 $231.73   3.426%   $239.6691   $239.67   $239.65   $239.70  
  Purchase #3 $166.78   8.157%   $180.3842   $180.38   $180.40   $180.40  
  Purchase #4 $175.29   3.379%   $181.213   $181.21   $181.20   $181.20  
  Purchase #5 $69.36   13.791%   $78.9254   $78.93   $78.95   $78.90  
  Purchase #6 $125.84   4.529%   $131.5393   $131.54   $131.55   $131.50  
  Purchase #7 $50.80   3.729%   $52.6943   $52.69   $52.70   $52.70  
  7 purchase totals = $882.11       $932.1818   $932.18   $932.20   $932.20