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 $244.48   9.419%   $267.5076   $267.51   $267.50   $267.50  
  Purchase #2 $162.91   4.662%   $170.5049   $170.50   $170.50   $170.50  
  Purchase #3 $248.52   5.726%   $262.7503   $262.75   $262.75   $262.80  
  Purchase #4 $29.39   4.313%   $30.6576   $30.66   $30.65   $30.70  
  Purchase #5 $96.83   7.534%   $104.1252   $104.13   $104.15   $104.10  
  Purchase #6 $42.48   11.435%   $47.3376   $47.34   $47.35   $47.30  
  Purchase #7 $142.37   3.121%   $146.8134   $146.81   $146.80   $146.80  
  7 purchase totals = $966.98       $1,029.6966   $1,029.70   $1,029.70   $1,029.70