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 $59.43   6.582%   $63.3417   $63.34   $63.35   $63.30  
  Purchase #2 $89.84   13.214%   $101.7115   $101.71   $101.70   $101.70  
  Purchase #3 $167.74   6.806%   $179.1564   $179.16   $179.15   $179.20  
  Purchase #4 $16.30   10.761%   $18.054   $18.05   $18.05   $18.10  
  Purchase #5 $205.79   10.471%   $227.3383   $227.34   $227.35   $227.30  
  Purchase #6 $135.53   13.793%   $154.2237   $154.22   $154.20   $154.20  
  Purchase #7 $49.54   8.160%   $53.5825   $53.58   $53.60   $53.60  
  7 purchase totals = $724.17       $797.4081   $797.40   $797.40   $797.40