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 $223.84   7.204%   $239.9654   $239.97   $239.95   $240.00  
  Purchase #2 $204.94   11.496%   $228.4999   $228.50   $228.50   $228.50  
  Purchase #3 $65.48   7.126%   $70.1461   $70.15   $70.15   $70.10  
  Purchase #4 $146.32   11.281%   $162.8264   $162.83   $162.85   $162.80  
  Purchase #5 $23.67   11.806%   $26.4645   $26.46   $26.45   $26.50  
  Purchase #6 $133.75   8.628%   $145.29   $145.29   $145.30   $145.30  
  Purchase #7 $180.99   8.130%   $195.7045   $195.70   $195.70   $195.70  
  7 purchase totals = $978.99       $1,068.8968   $1,068.90   $1,068.90   $1,068.90