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 $47.83   10.782%   $52.987   $52.99   $53.00   $53.00  
  Purchase #2 $123.38   9.567%   $135.1838   $135.18   $135.20   $135.20  
  Purchase #3 $43.30   5.713%   $45.7737   $45.77   $45.75   $45.80  
  Purchase #4 $64.78   8.572%   $70.3329   $70.33   $70.35   $70.30  
  Purchase #5 $228.33   3.126%   $235.4676   $235.47   $235.45   $235.50  
  Purchase #6 $183.56   5.757%   $194.1275   $194.13   $194.15   $194.10  
  Purchase #7 $35.46   4.696%   $37.1252   $37.13   $37.15   $37.10  
  7 purchase totals = $726.64       $770.9977   $771.00   $771.05   $771.00