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 $33.34   10.244%   $36.7553   $36.76   $36.75   $36.80  
  Purchase #2 $200.97   6.347%   $213.7256   $213.73   $213.75   $213.70  
  Purchase #3 $95.39   10.112%   $105.0358   $105.04   $105.05   $105.00  
  Purchase #4 $121.56   3.129%   $125.3636   $125.36   $125.35   $125.40  
  Purchase #5 $171.63   11.734%   $191.7691   $191.77   $191.75   $191.80  
  Purchase #6 $108.31   8.577%   $117.5997   $117.60   $117.60   $117.60  
  Purchase #7 $249.35   6.575%   $265.7448   $265.74   $265.75   $265.70  
  7 purchase totals = $980.55       $1,055.9939   $1,056.00   $1,056.00   $1,056.00