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 $239.29   12.262%   $268.6317   $268.63   $268.65   $268.60  
  Purchase #2 $42.54   5.151%   $44.7312   $44.73   $44.75   $44.70  
  Purchase #3 $82.38   11.301%   $91.6898   $91.69   $91.70   $91.70  
  Purchase #4 $184.74   6.671%   $197.064   $197.06   $197.05   $197.10  
  Purchase #5 $180.43   13.606%   $204.9793   $204.98   $205.00   $205.00  
  Purchase #6 $108.91   10.623%   $120.4795   $120.48   $120.50   $120.50  
  Purchase #7 $168.75   9.188%   $184.2548   $184.25   $184.25   $184.30  
  7 purchase totals = $1,007.04       $1,111.8303   $1,111.82   $1,111.90   $1,111.90