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 $203.74   12.269%   $228.7369   $228.74   $228.75   $228.70  
  Purchase #2 $130.28   5.850%   $137.9014   $137.90   $137.90   $137.90  
  Purchase #3 $119.44   12.240%   $134.0595   $134.06   $134.05   $134.10  
  Purchase #4 $218.66   6.626%   $233.1484   $233.15   $233.15   $233.10  
  Purchase #5 $203.71   9.358%   $222.7732   $222.77   $222.75   $222.80  
  Purchase #6 $78.80   5.790%   $83.3625   $83.36   $83.35   $83.40  
  Purchase #7 $50.74   8.446%   $55.0255   $55.03   $55.05   $55.00  
  7 purchase totals = $1,005.37       $1,095.0074   $1,095.01   $1,095.00   $1,095.00