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 $58.64   12.531%   $65.9882   $65.99   $66.00   $66.00  
  Purchase #2 $214.86   13.159%   $243.1334   $243.13   $243.15   $243.10  
  Purchase #3 $138.32   13.302%   $156.7193   $156.72   $156.70   $156.70  
  Purchase #4 $203.46   9.393%   $222.571   $222.57   $222.55   $222.60  
  Purchase #5 $147.81   4.179%   $153.987   $153.99   $154.00   $154.00  
  Purchase #6 $232.34   9.738%   $254.9653   $254.97   $254.95   $255.00  
  Purchase #7 $68.67   5.515%   $72.4572   $72.46   $72.45   $72.50  
  7 purchase totals = $1,064.10       $1,169.8214   $1,169.83   $1,169.80   $1,169.90