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 $244.50   7.522%   $262.8913   $262.89   $262.90   $262.90  
  Purchase #2 $85.35   9.193%   $93.1962   $93.20   $93.20   $93.20  
  Purchase #3 $137.50   13.377%   $155.8934   $155.89   $155.90   $155.90  
  Purchase #4 $123.92   11.565%   $138.2513   $138.25   $138.25   $138.30  
  Purchase #5 $72.68   7.105%   $77.8439   $77.84   $77.85   $77.80  
  Purchase #6 $61.59   9.812%   $67.6332   $67.63   $67.65   $67.60  
  Purchase #7 $193.95   4.728%   $203.12   $203.12   $203.10   $203.10  
  7 purchase totals = $919.49       $998.8293   $998.82   $998.85   $998.80