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 $189.44   13.246%   $214.5332   $214.53   $214.55   $214.50  
  Purchase #2 $52.29   11.307%   $58.2024   $58.20   $58.20   $58.20  
  Purchase #3 $70.82   4.227%   $73.8136   $73.81   $73.80   $73.80  
  Purchase #4 $174.81   13.105%   $197.7189   $197.72   $197.70   $197.70  
  Purchase #5 $223.90   9.205%   $244.51   $244.51   $244.50   $244.50  
  Purchase #6 $211.89   4.705%   $221.8594   $221.86   $221.85   $221.90  
  Purchase #7 $55.29   4.669%   $57.8715   $57.87   $57.85   $57.90  
  7 purchase totals = $978.44       $1,068.5090   $1,068.50   $1,068.45   $1,068.50