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	$7.80	13.663%	$8.8657	$8.87	$8.85	$8.90
Purchase #2	$157.95	9.738%	$173.3312	$173.33	$173.35	$173.30
Purchase #3	$163.65	7.242%	$175.5015	$175.50	$175.50	$175.50
Purchase #4	$160.48	12.578%	$180.6652	$180.67	$180.65	$180.70
Purchase #5	$114.71	10.864%	$127.1721	$127.17	$127.15	$127.20
Purchase #6	$89.53	3.196%	$92.3914	$92.39	$92.40	$92.40
Purchase #7	$221.54	9.790%	$243.2288	$243.23	$243.25	$243.20
7 purchase totals =	$915.66		$1,001.1559	$1,001.16	$1,001.15	$1,001.20