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	$37.89	13.251%	$42.9108	$42.91	$42.90	$42.90
Purchase #2	$26.92	6.662%	$28.7134	$28.71	$28.70	$28.70
Purchase #3	$248.59	8.828%	$270.5355	$270.54	$270.55	$270.50
Purchase #4	$230.49	11.296%	$256.5262	$256.53	$256.55	$256.50
Purchase #5	$218.94	12.317%	$245.9068	$245.91	$245.90	$245.90
Purchase #6	$67.71	4.827%	$70.9784	$70.98	$71.00	$71.00
Purchase #7	$183.68	8.334%	$198.9879	$198.99	$199.00	$199.00
7 purchase totals =	$1,014.22		$1,114.5590	$1,114.57	$1,114.60	$1,114.50