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 $104.44   11.294%   $116.2355   $116.24   $116.25   $116.20  
  Purchase #2 $222.63   3.610%   $230.6669   $230.67   $230.65   $230.70  
  Purchase #3 $133.79   7.244%   $143.4817   $143.48   $143.50   $143.50  
  Purchase #4 $243.58   13.872%   $277.3694   $277.37   $277.35   $277.40  
  Purchase #5 $173.43   3.164%   $178.9173   $178.92   $178.90   $178.90  
  Purchase #6 $197.33   8.647%   $214.3931   $214.39   $214.40   $214.40  
  Purchase #7 $42.77   12.289%   $48.026   $48.03   $48.05   $48.00  
  7 purchase totals = $1,117.97       $1,209.0899   $1,209.10   $1,209.10   $1,209.10