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 $58.33   12.615%   $65.6883   $65.69   $65.70   $65.70  
  Purchase #2 $199.32   5.368%   $210.0195   $210.02   $210.00   $210.00  
  Purchase #3 $67.84   4.505%   $70.8962   $70.90   $70.90   $70.90  
  Purchase #4 $134.50   4.225%   $140.1826   $140.18   $140.20   $140.20  
  Purchase #5 $186.97   10.229%   $206.0952   $206.10   $206.10   $206.10  
  Purchase #6 $233.65   4.524%   $244.2203   $244.22   $244.20   $244.20  
  Purchase #7 $143.67   13.105%   $162.498   $162.50   $162.50   $162.50  
  7 purchase totals = $1,024.28       $1,099.6001   $1,099.61   $1,099.60   $1,099.60