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 $184.70   10.473%   $204.0436   $204.04   $204.05   $204.00  
  Purchase #2 $85.37   11.527%   $95.2106   $95.21   $95.20   $95.20  
  Purchase #3 $125.91   3.299%   $130.0638   $130.06   $130.05   $130.10  
  Purchase #4 $59.88   10.159%   $65.9632   $65.96   $65.95   $66.00  
  Purchase #5 $94.91   4.206%   $98.9019   $98.90   $98.90   $98.90  
  Purchase #6 $88.81   6.804%   $94.8526   $94.85   $94.85   $94.90  
  Purchase #7 $100.60   5.294%   $105.9258   $105.93   $105.95   $105.90  
  7 purchase totals = $740.18       $794.9615   $794.95   $794.95   $795.00