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 $22.66   6.653%   $24.1676   $24.17   $24.15   $24.20  
  Purchase #2 $185.52   9.838%   $203.7715   $203.77   $203.75   $203.80  
  Purchase #3 $166.40   4.420%   $173.7549   $173.75   $173.75   $173.80  
  Purchase #4 $143.28   13.181%   $162.1657   $162.17   $162.15   $162.20  
  Purchase #5 $49.77   11.386%   $55.4368   $55.44   $55.45   $55.40  
  Purchase #6 $156.75   9.326%   $171.3685   $171.37   $171.35   $171.40  
  Purchase #7 $160.71   6.577%   $171.2799   $171.28   $171.30   $171.30  
  7 purchase totals = $885.09       $961.9449   $961.95   $961.90   $962.10