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 $176.89   13.614%   $200.9718   $200.97   $200.95   $201.00  
  Purchase #2 $188.65   3.853%   $195.9187   $195.92   $195.90   $195.90  
  Purchase #3 $214.73   11.844%   $240.1626   $240.16   $240.15   $240.20  
  Purchase #4 $142.92   5.202%   $150.3547   $150.35   $150.35   $150.40  
  Purchase #5 $141.81   7.487%   $152.4273   $152.43   $152.45   $152.40  
  Purchase #6 $58.35   8.782%   $63.4743   $63.47   $63.45   $63.50  
  Purchase #7 $22.55   9.258%   $24.6377   $24.64   $24.65   $24.60  
  7 purchase totals = $945.90       $1,027.9471   $1,027.94   $1,027.90   $1,028.00