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 $182.35   11.866%   $203.9877   $203.99   $204.00   $204.00  
  Purchase #2 $247.77   3.160%   $255.5995   $255.60   $255.60   $255.60  
  Purchase #3 $113.65   5.180%   $119.5371   $119.54   $119.55   $119.50  
  Purchase #4 $231.74   11.539%   $258.4805   $258.48   $258.50   $258.50  
  Purchase #5 $76.26   11.615%   $85.1176   $85.12   $85.10   $85.10  
  Purchase #6 $159.33   11.419%   $177.5239   $177.52   $177.50   $177.50  
  Purchase #7 $122.77   13.459%   $139.2936   $139.29   $139.30   $139.30  
  7 purchase totals = $1,133.87       $1,239.5399   $1,239.54   $1,239.55   $1,239.50