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 $147.29   4.734%   $154.2627   $154.26   $154.25   $154.30  
  Purchase #2 $71.38   6.266%   $75.8527   $75.85   $75.85   $75.90  
  Purchase #3 $220.97   8.778%   $240.3667   $240.37   $240.35   $240.40  
  Purchase #4 $23.30   4.256%   $24.2916   $24.29   $24.30   $24.30  
  Purchase #5 $93.35   4.203%   $97.2735   $97.27   $97.25   $97.30  
  Purchase #6 $77.79   5.553%   $82.1097   $82.11   $82.10   $82.10  
  Purchase #7 $227.36   4.466%   $237.5139   $237.51   $237.50   $237.50  
  7 purchase totals = $861.44       $911.6708   $911.66   $911.60   $911.80