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 $244.44   3.244%   $252.3696   $252.37   $252.35   $252.40  
  Purchase #2 $46.63   7.844%   $50.2877   $50.29   $50.30   $50.30  
  Purchase #3 $95.90   6.623%   $102.2515   $102.25   $102.25   $102.30  
  Purchase #4 $200.54   8.863%   $218.3139   $218.31   $218.30   $218.30  
  Purchase #5 $68.29   12.777%   $77.0154   $77.02   $77.00   $77.00  
  Purchase #6 $161.32   12.510%   $181.5011   $181.50   $181.50   $181.50  
  Purchase #7 $136.92   10.416%   $151.1816   $151.18   $151.20   $151.20  
  7 purchase totals = $954.04       $1,032.9208   $1,032.92   $1,032.90   $1,033.00