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 $72.63   9.222%   $79.3279   $79.33   $79.35   $79.30  
  Purchase #2 $114.77   6.334%   $122.0395   $122.04   $122.05   $122.00  
  Purchase #3 $133.81   5.737%   $141.4867   $141.49   $141.50   $141.50  
  Purchase #4 $234.31   8.328%   $253.8233   $253.82   $253.80   $253.80  
  Purchase #5 $198.62   13.129%   $224.6968   $224.70   $224.70   $224.70  
  Purchase #6 $53.81   12.153%   $60.3495   $60.35   $60.35   $60.30  
  Purchase #7 $145.40   5.414%   $153.272   $153.27   $153.25   $153.30  
  7 purchase totals = $953.35       $1,034.9957   $1,035.00   $1,035.00   $1,034.90