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 $186.63   7.861%   $201.301   $201.30   $201.30   $201.30  
  Purchase #2 $233.78   11.313%   $260.2275   $260.23   $260.25   $260.20  
  Purchase #3 $57.66   8.284%   $62.4366   $62.44   $62.45   $62.40  
  Purchase #4 $223.94   13.566%   $254.3197   $254.32   $254.30   $254.30  
  Purchase #5 $27.66   9.237%   $30.215   $30.22   $30.20   $30.20  
  Purchase #6 $127.69   13.245%   $144.6025   $144.60   $144.60   $144.60  
  Purchase #7 $171.57   12.112%   $192.3506   $192.35   $192.35   $192.40  
  7 purchase totals = $1,028.93       $1,145.4529   $1,145.46   $1,145.45   $1,145.40