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 $39.27   8.511%   $42.6123   $42.61   $42.60   $42.60  
  Purchase #2 $214.37   8.869%   $233.3825   $233.38   $233.40   $233.40  
  Purchase #3 $15.31   12.802%   $17.27   $17.27   $17.25   $17.30  
  Purchase #4 $103.55   6.331%   $110.1058   $110.11   $110.10   $110.10  
  Purchase #5 $203.42   5.234%   $214.067   $214.07   $214.05   $214.10  
  Purchase #6 $118.38   5.496%   $124.8862   $124.89   $124.90   $124.90  
  Purchase #7 $187.97   10.457%   $207.626   $207.63   $207.65   $207.60  
  7 purchase totals = $882.27       $949.9498   $949.96   $949.95   $950.00