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	$78.54	5.442%	$82.8141	$82.81	$82.80	$82.80
Purchase #2	$57.90	13.223%	$65.5561	$65.56	$65.55	$65.60
Purchase #3	$118.69	10.249%	$130.8545	$130.85	$130.85	$130.90
Purchase #4	$173.98	4.148%	$181.1967	$181.20	$181.20	$181.20
Purchase #5	$147.71	12.320%	$165.9079	$165.91	$165.90	$165.90
Purchase #6	$194.49	6.133%	$206.4181	$206.42	$206.40	$206.40
Purchase #7	$173.44	3.671%	$179.807	$179.81	$179.80	$179.80
7 purchase totals =	$944.75		$1,012.5544	$1,012.56	$1,012.50	$1,012.60