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 $61.85   6.174%   $65.6686   $65.67   $65.65   $65.70  
  Purchase #2 $224.77   12.702%   $253.3203   $253.32   $253.30   $253.30  
  Purchase #3 $61.41   10.236%   $67.6959   $67.70   $67.70   $67.70  
  Purchase #4 $58.76   5.804%   $62.1704   $62.17   $62.15   $62.20  
  Purchase #5 $196.74   5.602%   $207.7614   $207.76   $207.75   $207.80  
  Purchase #6 $100.81   9.662%   $110.5503   $110.55   $110.55   $110.60  
  Purchase #7 $239.58   4.243%   $249.7454   $249.75   $249.75   $249.70  
  7 purchase totals = $943.92       $1,016.9123   $1,016.92   $1,016.85   $1,017.00