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 $203.92   13.406%   $231.2575   $231.26   $231.25   $231.30  
  Purchase #2 $206.43   8.127%   $223.2066   $223.21   $223.20   $223.20  
  Purchase #3 $212.44   8.408%   $230.302   $230.30   $230.30   $230.30  
  Purchase #4 $228.31   12.398%   $256.6159   $256.62   $256.60   $256.60  
  Purchase #5 $242.31   9.439%   $265.1816   $265.18   $265.20   $265.20  
  Purchase #6 $61.53   12.342%   $69.124   $69.12   $69.10   $69.10  
  Purchase #7 $214.60   9.835%   $235.7059   $235.71   $235.70   $235.70  
  7 purchase totals = $1,369.54       $1,511.3935   $1,511.40   $1,511.35   $1,511.40