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 $183.69   5.715%   $194.1879   $194.19   $194.20   $194.20  
  Purchase #2 $98.26   7.272%   $105.4055   $105.41   $105.40   $105.40  
  Purchase #3 $152.36   11.270%   $169.531   $169.53   $169.55   $169.50  
  Purchase #4 $250.62   3.864%   $260.304   $260.30   $260.30   $260.30  
  Purchase #5 $243.73   10.324%   $268.8927   $268.89   $268.90   $268.90  
  Purchase #6 $40.34   6.202%   $42.8419   $42.84   $42.85   $42.80  
  Purchase #7 $171.78   7.597%   $184.8301   $184.83   $184.85   $184.80  
  7 purchase totals = $1,140.78       $1,225.9931   $1,225.99   $1,226.05   $1,225.90