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 $234.69   4.479%   $245.2018   $245.20   $245.20   $245.20  
  Purchase #2 $121.30   3.338%   $125.349   $125.35   $125.35   $125.30  
  Purchase #3 $247.37   7.131%   $265.01   $265.01   $265.00   $265.00  
  Purchase #4 $33.58   5.170%   $35.3161   $35.32   $35.30   $35.30  
  Purchase #5 $191.43   9.615%   $209.836   $209.84   $209.85   $209.80  
  Purchase #6 $202.51   5.806%   $214.2677   $214.27   $214.25   $214.30  
  Purchase #7 $140.67   13.307%   $159.389   $159.39   $159.40   $159.40  
  7 purchase totals = $1,171.55       $1,254.3696   $1,254.38   $1,254.35   $1,254.30