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 $108.97   10.146%   $120.0261   $120.03   $120.05   $120.00  
  Purchase #2 $101.89   5.764%   $107.7629   $107.76   $107.75   $107.80  
  Purchase #3 $88.92   4.786%   $93.1757   $93.18   $93.20   $93.20  
  Purchase #4 $126.74   6.725%   $135.2633   $135.26   $135.25   $135.30  
  Purchase #5 $88.52   11.393%   $98.6051   $98.61   $98.60   $98.60  
  Purchase #6 $46.30   8.826%   $50.3864   $50.39   $50.40   $50.40  
  Purchase #7 $144.40   7.494%   $155.2213   $155.22   $155.20   $155.20  
  7 purchase totals = $705.74       $760.4408   $760.45   $760.45   $760.50