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 $89.69   5.561%   $94.6777   $94.68   $94.70   $94.70  
  Purchase #2 $61.78   12.483%   $69.492   $69.49   $69.50   $69.50  
  Purchase #3 $79.65   7.493%   $85.6182   $85.62   $85.60   $85.60  
  Purchase #4 $115.25   7.195%   $123.5422   $123.54   $123.55   $123.50  
  Purchase #5 $239.90   10.851%   $265.9315   $265.93   $265.95   $265.90  
  Purchase #6 $140.85   5.198%   $148.1714   $148.17   $148.15   $148.20  
  Purchase #7 $50.29   8.701%   $54.6657   $54.67   $54.65   $54.70  
  7 purchase totals = $777.41       $842.0987   $842.10   $842.10   $842.10