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 $233.85   6.391%   $248.7954   $248.80   $248.80   $248.80  
  Purchase #2 $211.82   4.145%   $220.5999   $220.60   $220.60   $220.60  
  Purchase #3 $57.84   13.601%   $65.7068   $65.71   $65.70   $65.70  
  Purchase #4 $33.35   5.803%   $35.2853   $35.29   $35.30   $35.30  
  Purchase #5 $248.32   5.374%   $261.6647   $261.66   $261.65   $261.70  
  Purchase #6 $61.73   9.804%   $67.782   $67.78   $67.80   $67.80  
  Purchase #7 $77.80   6.755%   $83.0554   $83.06   $83.05   $83.10  
  7 purchase totals = $924.71       $982.8895   $982.90   $982.90   $983.00