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 $230.27   7.806%   $248.2449   $248.24   $248.25   $248.20  
  Purchase #2 $176.31   10.353%   $194.5634   $194.56   $194.55   $194.60  
  Purchase #3 $214.83   6.698%   $229.2193   $229.22   $229.20   $229.20  
  Purchase #4 $245.46   5.320%   $258.5185   $258.52   $258.50   $258.50  
  Purchase #5 $207.71   3.748%   $215.495   $215.50   $215.50   $215.50  
  Purchase #6 $16.81   5.655%   $17.7606   $17.76   $17.75   $17.80  
  Purchase #7 $211.50   3.779%   $219.4926   $219.49   $219.50   $219.50  
  7 purchase totals = $1,302.89       $1,383.2943   $1,383.29   $1,383.25   $1,383.30