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 $147.32   5.599%   $155.5684   $155.57   $155.55   $155.60  
  Purchase #2 $39.67   9.185%   $43.3137   $43.31   $43.30   $43.30  
  Purchase #3 $79.88   3.273%   $82.4945   $82.49   $82.50   $82.50  
  Purchase #4 $162.25   4.476%   $169.5123   $169.51   $169.50   $169.50  
  Purchase #5 $175.76   5.526%   $185.4725   $185.47   $185.45   $185.50  
  Purchase #6 $59.76   7.184%   $64.0532   $64.05   $64.05   $64.10  
  Purchase #7 $144.99   12.636%   $163.3109   $163.31   $163.30   $163.30  
  7 purchase totals = $809.63       $863.7255   $863.71   $863.65   $863.80