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 $205.35   8.752%   $223.3222   $223.32   $223.30   $223.30  
  Purchase #2 $217.58   4.482%   $227.3319   $227.33   $227.35   $227.30  
  Purchase #3 $86.85   12.471%   $97.6811   $97.68   $97.70   $97.70  
  Purchase #4 $164.27   11.242%   $182.7372   $182.74   $182.75   $182.70  
  Purchase #5 $200.96   5.332%   $211.6752   $211.68   $211.70   $211.70  
  Purchase #6 $186.95   7.345%   $200.6815   $200.68   $200.70   $200.70  
  Purchase #7 $196.93   4.831%   $206.4437   $206.44   $206.45   $206.40  
  7 purchase totals = $1,258.89       $1,349.8728   $1,349.87   $1,349.95   $1,349.80