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 $117.56   6.601%   $125.3201   $125.32   $125.30   $125.30  
  Purchase #2 $93.87   9.838%   $103.1049   $103.10   $103.10   $103.10  
  Purchase #3 $115.96   8.578%   $125.907   $125.91   $125.90   $125.90  
  Purchase #4 $91.60   4.196%   $95.4435   $95.44   $95.45   $95.40  
  Purchase #5 $190.94   5.412%   $201.2737   $201.27   $201.25   $201.30  
  Purchase #6 $127.32   11.510%   $141.9745   $141.97   $141.95   $142.00  
  Purchase #7 $232.99   10.685%   $257.885   $257.89   $257.90   $257.90  
  7 purchase totals = $970.24       $1,050.9087   $1,050.90   $1,050.85   $1,050.90