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 $243.89   10.379%   $269.2033   $269.20   $269.20   $269.20  
  Purchase #2 $223.95   13.288%   $253.7085   $253.71   $253.70   $253.70  
  Purchase #3 $53.86   13.703%   $61.2404   $61.24   $61.25   $61.20  
  Purchase #4 $147.74   13.140%   $167.153   $167.15   $167.15   $167.20  
  Purchase #5 $215.34   13.361%   $244.1116   $244.11   $244.10   $244.10  
  Purchase #6 $162.27   11.236%   $180.5027   $180.50   $180.50   $180.50  
  Purchase #7 $234.25   8.355%   $253.8216   $253.82   $253.80   $253.80  
  7 purchase totals = $1,281.30       $1,429.7411   $1,429.73   $1,429.70   $1,429.70