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 $34.43   6.104%   $36.5316   $36.53   $36.55   $36.50  
  Purchase #2 $51.52   4.856%   $54.0218   $54.02   $54.00   $54.00  
  Purchase #3 $59.60   7.643%   $64.1552   $64.16   $64.15   $64.20  
  Purchase #4 $204.77   9.838%   $224.9153   $224.92   $224.90   $224.90  
  Purchase #5 $92.44   8.722%   $100.5026   $100.50   $100.50   $100.50  
  Purchase #6 $234.48   7.366%   $251.7518   $251.75   $251.75   $251.80  
  Purchase #7 $199.97   13.278%   $226.522   $226.52   $226.50   $226.50  
  7 purchase totals = $877.21       $958.4003   $958.40   $958.35   $958.40