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 $56.86   7.771%   $61.2786   $61.28   $61.30   $61.30  
  Purchase #2 $206.64   7.319%   $221.764   $221.76   $221.75   $221.80  
  Purchase #3 $220.85   13.174%   $249.9448   $249.94   $249.95   $249.90  
  Purchase #4 $184.58   5.214%   $194.204   $194.20   $194.20   $194.20  
  Purchase #5 $58.31   5.213%   $61.3497   $61.35   $61.35   $61.30  
  Purchase #6 $158.90   7.324%   $170.5378   $170.54   $170.55   $170.50  
  Purchase #7 $48.86   11.727%   $54.5898   $54.59   $54.60   $54.60  
  7 purchase totals = $935.00       $1,013.6687   $1,013.66   $1,013.70   $1,013.60