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 $44.53   8.246%   $48.2019   $48.20   $48.20   $48.20  
  Purchase #2 $165.28   8.339%   $179.0627   $179.06   $179.05   $179.10  
  Purchase #3 $137.79   9.560%   $150.9627   $150.96   $150.95   $151.00  
  Purchase #4 $12.76   11.794%   $14.2649   $14.26   $14.25   $14.30  
  Purchase #5 $64.96   11.865%   $72.6675   $72.67   $72.65   $72.70  
  Purchase #6 $228.35   3.687%   $236.7693   $236.77   $236.75   $236.80  
  Purchase #7 $46.91   7.512%   $50.4339   $50.43   $50.45   $50.40  
  7 purchase totals = $700.58       $752.3629   $752.35   $752.30   $752.50