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 $241.29   11.157%   $268.2107   $268.21   $268.20   $268.20  
  Purchase #2 $176.82   9.449%   $193.5277   $193.53   $193.55   $193.50  
  Purchase #3 $235.33   7.504%   $252.9892   $252.99   $253.00   $253.00  
  Purchase #4 $62.56   3.268%   $64.6045   $64.60   $64.60   $64.60  
  Purchase #5 $221.81   9.726%   $243.3832   $243.38   $243.40   $243.40  
  Purchase #6 $227.79   4.862%   $238.8651   $238.87   $238.85   $238.90  
  Purchase #7 $64.62   6.514%   $68.8293   $68.83   $68.85   $68.80  
  7 purchase totals = $1,230.22       $1,330.4097   $1,330.41   $1,330.45   $1,330.40