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 $42.32   3.800%   $43.9282   $43.93   $43.95   $43.90  
  Purchase #2 $175.52   12.424%   $197.3266   $197.33   $197.35   $197.30  
  Purchase #3 $61.56   4.495%   $64.3271   $64.33   $64.35   $64.30  
  Purchase #4 $116.70   9.517%   $127.8063   $127.81   $127.80   $127.80  
  Purchase #5 $46.45   10.523%   $51.3379   $51.34   $51.35   $51.30  
  Purchase #6 $205.92   10.141%   $226.8023   $226.80   $226.80   $226.80  
  Purchase #7 $198.77   12.826%   $224.2642   $224.26   $224.25   $224.30  
  7 purchase totals = $847.24       $935.7926   $935.80   $935.85   $935.70