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 $245.35   3.825%   $254.7346   $254.73   $254.75   $254.70  
  Purchase #2 $6.39   3.253%   $6.5979   $6.60   $6.60   $6.60  
  Purchase #3 $206.79   3.434%   $213.8912   $213.89   $213.90   $213.90  
  Purchase #4 $90.97   8.136%   $98.3713   $98.37   $98.35   $98.40  
  Purchase #5 $189.86   11.376%   $211.4585   $211.46   $211.45   $211.50  
  Purchase #6 $213.85   13.708%   $243.1646   $243.16   $243.15   $243.20  
  Purchase #7 $25.42   3.697%   $26.3598   $26.36   $26.35   $26.40  
  7 purchase totals = $978.63       $1,054.5779   $1,054.57   $1,054.55   $1,054.70