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 $48.55   3.544%   $50.2706   $50.27   $50.25   $50.30  
  Purchase #2 $201.33   8.579%   $218.6021   $218.60   $218.60   $218.60  
  Purchase #3 $246.73   7.539%   $265.331   $265.33   $265.35   $265.30  
  Purchase #4 $97.47   10.395%   $107.602   $107.60   $107.60   $107.60  
  Purchase #5 $81.26   5.260%   $85.5343   $85.53   $85.55   $85.50  
  Purchase #6 $67.29   7.140%   $72.0945   $72.09   $72.10   $72.10  
  Purchase #7 $214.92   5.748%   $227.2736   $227.27   $227.25   $227.30  
  7 purchase totals = $957.55       $1,026.7081   $1,026.69   $1,026.70   $1,026.70