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 $220.53   9.620%   $241.745   $241.75   $241.75   $241.70  
  Purchase #2 $59.77   7.515%   $64.2617   $64.26   $64.25   $64.30  
  Purchase #3 $147.47   6.202%   $156.6161   $156.62   $156.60   $156.60  
  Purchase #4 $216.87   13.561%   $246.2797   $246.28   $246.30   $246.30  
  Purchase #5 $59.25   6.340%   $63.0065   $63.01   $63.00   $63.00  
  Purchase #6 $23.66   5.138%   $24.8757   $24.88   $24.90   $24.90  
  Purchase #7 $36.72   8.754%   $39.9345   $39.93   $39.95   $39.90  
  7 purchase totals = $764.27       $836.7192   $836.73   $836.75   $836.70