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 $190.38   10.278%   $209.9473   $209.95   $209.95   $209.90  
  Purchase #2 $57.39   5.720%   $60.6727   $60.67   $60.65   $60.70  
  Purchase #3 $69.74   6.672%   $74.3931   $74.39   $74.40   $74.40  
  Purchase #4 $33.78   10.467%   $37.3158   $37.32   $37.30   $37.30  
  Purchase #5 $89.33   9.743%   $98.0334   $98.03   $98.05   $98.00  
  Purchase #6 $116.48   8.496%   $126.3761   $126.38   $126.40   $126.40  
  Purchase #7 $237.57   5.661%   $251.0188   $251.02   $251.00   $251.00  
  7 purchase totals = $794.67       $857.7572   $857.76   $857.75   $857.70