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 $124.75   7.698%   $134.3533   $134.35   $134.35   $134.40  
  Purchase #2 $200.27   10.166%   $220.6294   $220.63   $220.65   $220.60  
  Purchase #3 $70.67   11.664%   $78.9129   $78.91   $78.90   $78.90  
  Purchase #4 $65.99   13.191%   $74.6947   $74.69   $74.70   $74.70  
  Purchase #5 $199.57   6.232%   $212.0072   $212.01   $212.00   $212.00  
  Purchase #6 $239.44   8.174%   $259.0118   $259.01   $259.00   $259.00  
  Purchase #7 $8.72   13.188%   $9.87   $9.87   $9.85   $9.90  
  7 purchase totals = $909.41       $989.4793   $989.47   $989.45   $989.50