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 $151.87   10.720%   $168.1505   $168.15   $168.15   $168.20  
  Purchase #2 $229.69   12.610%   $258.6539   $258.65   $258.65   $258.70  
  Purchase #3 $212.85   5.580%   $224.727   $224.73   $224.75   $224.70  
  Purchase #4 $115.62   13.819%   $131.5975   $131.60   $131.60   $131.60  
  Purchase #5 $247.70   13.491%   $281.1172   $281.12   $281.10   $281.10  
  Purchase #6 $28.69   7.277%   $30.7778   $30.78   $30.80   $30.80  
  Purchase #7 $131.87   10.539%   $145.7678   $145.77   $145.75   $145.80  
  7 purchase totals = $1,118.29       $1,240.7917   $1,240.80   $1,240.80   $1,240.90