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 $233.67   3.566%   $242.0027   $242.00   $242.00   $242.00  
  Purchase #2 $172.85   3.234%   $178.44   $178.44   $178.45   $178.40  
  Purchase #3 $113.51   3.538%   $117.526   $117.53   $117.55   $117.50  
  Purchase #4 $27.31   11.130%   $30.3496   $30.35   $30.35   $30.30  
  Purchase #5 $236.37   8.226%   $255.8138   $255.81   $255.80   $255.80  
  Purchase #6 $29.98   12.537%   $33.7386   $33.74   $33.75   $33.70  
  Purchase #7 $166.89   11.250%   $185.6651   $185.67   $185.65   $185.70  
  7 purchase totals = $980.58       $1,043.5358   $1,043.54   $1,043.55   $1,043.40