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 $62.39   13.178%   $70.6118   $70.61   $70.60   $70.60  
  Purchase #2 $130.96   6.599%   $139.6021   $139.60   $139.60   $139.60  
  Purchase #3 $74.37   10.192%   $81.9498   $81.95   $81.95   $81.90  
  Purchase #4 $246.58   5.599%   $260.386   $260.39   $260.40   $260.40  
  Purchase #5 $69.54   3.638%   $72.0699   $72.07   $72.05   $72.10  
  Purchase #6 $221.59   12.158%   $248.5309   $248.53   $248.55   $248.50  
  Purchase #7 $118.43   12.488%   $133.2195   $133.22   $133.20   $133.20  
  7 purchase totals = $923.86       $1,006.3700   $1,006.37   $1,006.35   $1,006.30