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 $215.98   9.390%   $236.2605   $236.26   $236.25   $236.30  
  Purchase #2 $135.41   6.255%   $143.8799   $143.88   $143.90   $143.90  
  Purchase #3 $137.28   10.172%   $151.2441   $151.24   $151.25   $151.20  
  Purchase #4 $210.92   4.453%   $220.3123   $220.31   $220.30   $220.30  
  Purchase #5 $127.84   9.137%   $139.5207   $139.52   $139.50   $139.50  
  Purchase #6 $49.58   5.761%   $52.4363   $52.44   $52.45   $52.40  
  Purchase #7 $233.33   13.444%   $264.6989   $264.70   $264.70   $264.70  
  7 purchase totals = $1,110.34       $1,208.3527   $1,208.35   $1,208.35   $1,208.30