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 $61.25   9.701%   $67.1919   $67.19   $67.20   $67.20  
  Purchase #2 $28.59   4.845%   $29.9752   $29.98   $30.00   $30.00  
  Purchase #3 $59.39   7.240%   $63.6898   $63.69   $63.70   $63.70  
  Purchase #4 $77.34   6.528%   $82.3888   $82.39   $82.40   $82.40  
  Purchase #5 $243.73   11.584%   $271.9637   $271.96   $271.95   $272.00  
  Purchase #6 $197.85   6.353%   $210.4194   $210.42   $210.40   $210.40  
  Purchase #7 $228.83   7.586%   $246.189   $246.19   $246.20   $246.20  
  7 purchase totals = $896.98       $971.8178   $971.82   $971.85   $971.90