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	$240.68	12.260%	$270.1874	$270.19	$270.20	$270.20
Purchase #2	$218.52	6.834%	$233.4537	$233.45	$233.45	$233.50
Purchase #3	$94.55	5.145%	$99.4146	$99.41	$99.40	$99.40
Purchase #4	$72.82	13.186%	$82.422	$82.42	$82.40	$82.40
Purchase #5	$67.57	13.208%	$76.4946	$76.49	$76.50	$76.50
Purchase #6	$209.64	6.120%	$222.47	$222.47	$222.45	$222.50
Purchase #7	$37.76	3.638%	$39.1337	$39.13	$39.15	$39.10
7 purchase totals =	$941.54		$1,023.5760	$1,023.56	$1,023.55	$1,023.60