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 $169.94   7.282%   $182.315   $182.32   $182.30   $182.30  
  Purchase #2 $61.58   5.842%   $65.1775   $65.18   $65.20   $65.20  
  Purchase #3 $213.45   6.778%   $227.9176   $227.92   $227.90   $227.90  
  Purchase #4 $176.76   9.346%   $193.28   $193.28   $193.30   $193.30  
  Purchase #5 $77.92   5.477%   $82.1877   $82.19   $82.20   $82.20  
  Purchase #6 $140.88   7.506%   $151.4545   $151.45   $151.45   $151.50  
  Purchase #7 $141.77   11.665%   $158.3075   $158.31   $158.30   $158.30  
  7 purchase totals = $982.30       $1,060.6398   $1,060.65   $1,060.65   $1,060.70