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 $232.83   5.773%   $246.2713   $246.27   $246.25   $246.30  
  Purchase #2 $116.97   8.371%   $126.7616   $126.76   $126.75   $126.80  
  Purchase #3 $73.31   4.319%   $76.4763   $76.48   $76.50   $76.50  
  Purchase #4 $8.48   3.236%   $8.7544   $8.75   $8.75   $8.80  
  Purchase #5 $80.47   9.425%   $88.0543   $88.05   $88.05   $88.10  
  Purchase #6 $130.55   5.218%   $137.3621   $137.36   $137.35   $137.40  
  Purchase #7 $240.30   10.287%   $265.0197   $265.02   $265.00   $265.00  
  7 purchase totals = $882.91       $948.6997   $948.69   $948.65   $948.90