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 $32.39   3.507%   $33.5259   $33.53   $33.55   $33.50  
  Purchase #2 $87.69   8.415%   $95.0691   $95.07   $95.05   $95.10  
  Purchase #3 $205.30   5.471%   $216.532   $216.53   $216.55   $216.50  
  Purchase #4 $127.58   6.806%   $136.2631   $136.26   $136.25   $136.30  
  Purchase #5 $214.27   7.536%   $230.4174   $230.42   $230.40   $230.40  
  Purchase #6 $22.74   8.276%   $24.622   $24.62   $24.60   $24.60  
  Purchase #7 $94.74   5.119%   $99.5897   $99.59   $99.60   $99.60  
  7 purchase totals = $784.71       $836.0192   $836.02   $836.00   $836.00