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 $193.59   11.374%   $215.6089   $215.61   $215.60   $215.60  
  Purchase #2 $162.41   9.441%   $177.7431   $177.74   $177.75   $177.70  
  Purchase #3 $195.31   5.234%   $205.5325   $205.53   $205.55   $205.50  
  Purchase #4 $146.38   11.211%   $162.7907   $162.79   $162.80   $162.80  
  Purchase #5 $30.48   8.176%   $32.972   $32.97   $32.95   $33.00  
  Purchase #6 $152.35   12.285%   $171.0662   $171.07   $171.05   $171.10  
  Purchase #7 $235.49   5.555%   $248.5715   $248.57   $248.55   $248.60  
  7 purchase totals = $1,116.01       $1,214.2849   $1,214.28   $1,214.25   $1,214.30