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 $231.44   10.442%   $255.607   $255.61   $255.60   $255.60  
  Purchase #2 $54.87   11.583%   $61.2256   $61.23   $61.25   $61.20  
  Purchase #3 $243.59   11.771%   $272.263   $272.26   $272.25   $272.30  
  Purchase #4 $130.98   3.377%   $135.4032   $135.40   $135.40   $135.40  
  Purchase #5 $131.34   3.507%   $135.9461   $135.95   $135.95   $135.90  
  Purchase #6 $179.25   6.838%   $191.5071   $191.51   $191.50   $191.50  
  Purchase #7 $161.94   4.349%   $168.9828   $168.98   $169.00   $169.00  
  7 purchase totals = $1,133.41       $1,220.9348   $1,220.94   $1,220.95   $1,220.90