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 $67.90   4.174%   $70.7341   $70.73   $70.75   $70.70  
  Purchase #2 $96.33   8.172%   $104.2021   $104.20   $104.20   $104.20  
  Purchase #3 $19.61   7.121%   $21.0064   $21.01   $21.00   $21.00  
  Purchase #4 $50.53   5.823%   $53.4724   $53.47   $53.45   $53.50  
  Purchase #5 $217.76   13.846%   $247.911   $247.91   $247.90   $247.90  
  Purchase #6 $224.69   10.717%   $248.77   $248.77   $248.75   $248.80  
  Purchase #7 $235.51   5.704%   $248.9435   $248.94   $248.95   $248.90  
  7 purchase totals = $912.33       $995.0395   $995.03   $995.00   $995.00