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 $90.76   4.170%   $94.5447   $94.54   $94.55   $94.50  
  Purchase #2 $149.62   3.735%   $155.2083   $155.21   $155.20   $155.20  
  Purchase #3 $232.35   11.773%   $259.7046   $259.70   $259.70   $259.70  
  Purchase #4 $49.70   10.232%   $54.7853   $54.79   $54.80   $54.80  
  Purchase #5 $23.29   8.856%   $25.3526   $25.35   $25.35   $25.40  
  Purchase #6 $185.53   6.212%   $197.0551   $197.06   $197.05   $197.10  
  Purchase #7 $26.36   5.789%   $27.886   $27.89   $27.90   $27.90  
  7 purchase totals = $757.61       $814.5366   $814.54   $814.55   $814.60