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 $65.89   13.596%   $74.8484   $74.85   $74.85   $74.80  
  Purchase #2 $57.76   7.726%   $62.2225   $62.22   $62.20   $62.20  
  Purchase #3 $151.83   5.572%   $160.29   $160.29   $160.30   $160.30  
  Purchase #4 $138.52   13.727%   $157.5346   $157.53   $157.55   $157.50  
  Purchase #5 $65.40   12.743%   $73.7339   $73.73   $73.75   $73.70  
  Purchase #6 $136.53   4.567%   $142.7653   $142.77   $142.75   $142.80  
  Purchase #7 $162.74   8.756%   $176.9895   $176.99   $177.00   $177.00  
  7 purchase totals = $778.67       $848.3842   $848.38   $848.40   $848.30