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 $119.70   3.249%   $123.5891   $123.59   $123.60   $123.60  
  Purchase #2 $84.35   9.227%   $92.133   $92.13   $92.15   $92.10  
  Purchase #3 $11.99   8.539%   $13.0138   $13.01   $13.00   $13.00  
  Purchase #4 $232.89   4.738%   $243.9243   $243.92   $243.90   $243.90  
  Purchase #5 $55.97   12.802%   $63.1353   $63.14   $63.15   $63.10  
  Purchase #6 $242.62   12.653%   $273.3187   $273.32   $273.30   $273.30  
  Purchase #7 $171.48   10.199%   $188.9692   $188.97   $188.95   $189.00  
  7 purchase totals = $919.00       $998.0834   $998.08   $998.05   $998.00