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 $137.30   4.229%   $143.1064   $143.11   $143.10   $143.10  
  Purchase #2 $178.52   11.497%   $199.0444   $199.04   $199.05   $199.00  
  Purchase #3 $151.39   4.271%   $157.8559   $157.86   $157.85   $157.90  
  Purchase #4 $26.94   13.340%   $30.5338   $30.53   $30.55   $30.50  
  Purchase #5 $203.36   8.374%   $220.3894   $220.39   $220.40   $220.40  
  Purchase #6 $201.34   9.351%   $220.1673   $220.17   $220.15   $220.20  
  Purchase #7 $237.28   6.648%   $253.0544   $253.05   $253.05   $253.10  
  7 purchase totals = $1,136.13       $1,224.1516   $1,224.15   $1,224.15   $1,224.20