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 $62.60   13.186%   $70.8544   $70.85   $70.85   $70.90  
  Purchase #2 $56.66   3.596%   $58.6975   $58.70   $58.70   $58.70  
  Purchase #3 $158.46   5.597%   $167.329   $167.33   $167.35   $167.30  
  Purchase #4 $200.49   10.377%   $221.2948   $221.29   $221.30   $221.30  
  Purchase #5 $113.91   4.122%   $118.6054   $118.61   $118.60   $118.60  
  Purchase #6 $132.68   8.858%   $144.4328   $144.43   $144.45   $144.40  
  Purchase #7 $235.41   4.841%   $246.8062   $246.81   $246.80   $246.80  
  7 purchase totals = $960.21       $1,028.0201   $1,028.02   $1,028.05   $1,028.00