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	$241.48	3.695%	$250.4027	$250.40	$250.40	$250.40
Purchase #2	$107.48	9.690%	$117.8948	$117.89	$117.90	$117.90
Purchase #3	$217.72	4.456%	$227.4216	$227.42	$227.40	$227.40
Purchase #4	$53.85	7.481%	$57.8785	$57.88	$57.90	$57.90
Purchase #5	$203.71	9.402%	$222.8628	$222.86	$222.85	$222.90
Purchase #6	$170.55	6.242%	$181.1957	$181.20	$181.20	$181.20
Purchase #7	$134.86	5.664%	$142.4985	$142.50	$142.50	$142.50
7 purchase totals =	$1,129.65		$1,200.1546	$1,200.15	$1,200.15	$1,200.20