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 $121.65   4.242%   $126.8104   $126.81   $126.80   $126.80  
  Purchase #2 $238.97   6.245%   $253.8937   $253.89   $253.90   $253.90  
  Purchase #3 $172.69   7.873%   $186.2859   $186.29   $186.30   $186.30  
  Purchase #4 $241.91   11.339%   $269.3402   $269.34   $269.35   $269.30  
  Purchase #5 $249.72   8.564%   $271.106   $271.11   $271.10   $271.10  
  Purchase #6 $12.79   6.502%   $13.6216   $13.62   $13.60   $13.60  
  Purchase #7 $28.62   12.607%   $32.2281   $32.23   $32.25   $32.20  
  7 purchase totals = $1,066.35       $1,153.2859   $1,153.29   $1,153.30   $1,153.20