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 $204.32   13.525%   $231.9543   $231.95   $231.95   $232.00  
  Purchase #2 $227.97   3.452%   $235.8395   $235.84   $235.85   $235.80  
  Purchase #3 $195.95   4.312%   $204.3994   $204.40   $204.40   $204.40  
  Purchase #4 $174.71   9.196%   $190.7763   $190.78   $190.80   $190.80  
  Purchase #5 $98.55   9.839%   $108.2463   $108.25   $108.25   $108.20  
  Purchase #6 $166.80   6.769%   $178.0907   $178.09   $178.10   $178.10  
  Purchase #7 $196.90   12.678%   $221.863   $221.86   $221.85   $221.90  
  7 purchase totals = $1,265.20       $1,371.1695   $1,371.17   $1,371.20   $1,371.20