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 $117.74   4.764%   $123.3491   $123.35   $123.35   $123.30  
  Purchase #2 $243.60   9.374%   $266.4351   $266.44   $266.45   $266.40  
  Purchase #3 $177.73   6.105%   $188.5804   $188.58   $188.60   $188.60  
  Purchase #4 $242.35   6.311%   $257.6447   $257.64   $257.65   $257.60  
  Purchase #5 $19.36   10.647%   $21.4213   $21.42   $21.40   $21.40  
  Purchase #6 $195.89   9.127%   $213.7689   $213.77   $213.75   $213.80  
  Purchase #7 $56.47   7.191%   $60.5308   $60.53   $60.55   $60.50  
  7 purchase totals = $1,053.14       $1,131.7303   $1,131.73   $1,131.75   $1,131.60