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 $67.34   13.403%   $76.3656   $76.37   $76.35   $76.40  
  Purchase #2 $105.98   7.316%   $113.7335   $113.73   $113.75   $113.70  
  Purchase #3 $141.34   6.237%   $150.1554   $150.16   $150.15   $150.20  
  Purchase #4 $172.89   5.436%   $182.2883   $182.29   $182.30   $182.30  
  Purchase #5 $61.50   6.190%   $65.3069   $65.31   $65.30   $65.30  
  Purchase #6 $197.26   4.757%   $206.6437   $206.64   $206.65   $206.60  
  Purchase #7 $238.44   3.109%   $245.8531   $245.85   $245.85   $245.90  
  7 purchase totals = $984.75       $1,040.3465   $1,040.35   $1,040.35   $1,040.40