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 $213.61   8.595%   $231.9698   $231.97   $231.95   $232.00  
  Purchase #2 $113.93   8.790%   $123.9444   $123.94   $123.95   $123.90  
  Purchase #3 $61.93   6.129%   $65.7257   $65.73   $65.75   $65.70  
  Purchase #4 $153.74   6.194%   $163.2627   $163.26   $163.25   $163.30  
  Purchase #5 $218.96   4.442%   $228.6862   $228.69   $228.70   $228.70  
  Purchase #6 $183.38   11.405%   $204.2945   $204.29   $204.30   $204.30  
  Purchase #7 $231.66   10.441%   $255.8476   $255.85   $255.85   $255.80  
  7 purchase totals = $1,177.21       $1,273.7309   $1,273.73   $1,273.75   $1,273.70