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 $155.59   10.491%   $171.9129   $171.91   $171.90   $171.90  
  Purchase #2 $192.62   6.223%   $204.6067   $204.61   $204.60   $204.60  
  Purchase #3 $95.59   8.119%   $103.351   $103.35   $103.35   $103.40  
  Purchase #4 $214.30   10.425%   $236.6408   $236.64   $236.65   $236.60  
  Purchase #5 $193.76   8.592%   $210.4079   $210.41   $210.40   $210.40  
  Purchase #6 $60.68   3.193%   $62.6175   $62.62   $62.60   $62.60  
  Purchase #7 $194.28   3.351%   $200.7903   $200.79   $200.80   $200.80  
  7 purchase totals = $1,106.82       $1,190.3271   $1,190.33   $1,190.30   $1,190.30