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 $103.70   12.750%   $116.9218   $116.92   $116.90   $116.90  
  Purchase #2 $137.64   7.330%   $147.729   $147.73   $147.75   $147.70  
  Purchase #3 $209.77   4.514%   $219.239   $219.24   $219.25   $219.20  
  Purchase #4 $84.45   3.515%   $87.4184   $87.42   $87.40   $87.40  
  Purchase #5 $215.84   4.497%   $225.5463   $225.55   $225.55   $225.50  
  Purchase #6 $62.48   12.859%   $70.5143   $70.51   $70.50   $70.50  
  Purchase #7 $66.37   5.301%   $69.8883   $69.89   $69.90   $69.90  
  7 purchase totals = $880.25       $937.2571   $937.26   $937.25   $937.10