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 $197.44   3.424%   $204.2003   $204.20   $204.20   $204.20  
  Purchase #2 $10.73   10.595%   $11.8668   $11.87   $11.85   $11.90  
  Purchase #3 $92.81   10.405%   $102.4669   $102.47   $102.45   $102.50  
  Purchase #4 $49.67   6.770%   $53.0327   $53.03   $53.05   $53.00  
  Purchase #5 $234.67   13.412%   $266.1439   $266.14   $266.15   $266.10  
  Purchase #6 $60.86   13.691%   $69.1923   $69.19   $69.20   $69.20  
  Purchase #7 $156.93   13.859%   $178.6789   $178.68   $178.70   $178.70  
  7 purchase totals = $803.11       $885.5818   $885.58   $885.60   $885.60