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 $239.83   6.352%   $255.064   $255.06   $255.05   $255.10  
  Purchase #2 $212.52   6.478%   $226.287   $226.29   $226.30   $226.30  
  Purchase #3 $167.46   3.722%   $173.6929   $173.69   $173.70   $173.70  
  Purchase #4 $219.99   11.595%   $245.4978   $245.50   $245.50   $245.50  
  Purchase #5 $203.44   10.503%   $224.8073   $224.81   $224.80   $224.80  
  Purchase #6 $112.61   4.121%   $117.2507   $117.25   $117.25   $117.30  
  Purchase #7 $236.35   8.142%   $255.5936   $255.59   $255.60   $255.60  
  7 purchase totals = $1,392.20       $1,498.1933   $1,498.19   $1,498.20   $1,498.30