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 $97.87   13.751%   $111.3281   $111.33   $111.35   $111.30  
  Purchase #2 $176.67   3.542%   $182.9277   $182.93   $182.95   $182.90  
  Purchase #3 $121.76   11.871%   $136.2141   $136.21   $136.20   $136.20  
  Purchase #4 $211.61   12.220%   $237.4687   $237.47   $237.45   $237.50  
  Purchase #5 $243.48   9.191%   $265.8582   $265.86   $265.85   $265.90  
  Purchase #6 $184.71   4.401%   $192.8391   $192.84   $192.85   $192.80  
  Purchase #7 $191.71   10.205%   $211.274   $211.27   $211.25   $211.30  
  7 purchase totals = $1,227.81       $1,337.9099   $1,337.91   $1,337.90   $1,337.90