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 $115.88   8.841%   $126.125   $126.13   $126.15   $126.10  
  Purchase #2 $142.35   5.420%   $150.0654   $150.07   $150.05   $150.10  
  Purchase #3 $59.98   4.175%   $62.4842   $62.48   $62.50   $62.50  
  Purchase #4 $174.87   4.268%   $182.3335   $182.33   $182.35   $182.30  
  Purchase #5 $231.62   5.567%   $244.5143   $244.51   $244.50   $244.50  
  Purchase #6 $27.48   6.772%   $29.3409   $29.34   $29.35   $29.30  
  Purchase #7 $226.62   9.719%   $248.6452   $248.65   $248.65   $248.60  
  7 purchase totals = $978.80       $1,043.5085   $1,043.51   $1,043.55   $1,043.40