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	$67.34	6.755%	$71.8888	$71.89	$71.90	$71.90
Purchase #2	$181.90	3.748%	$188.7176	$188.72	$188.70	$188.70
Purchase #3	$229.53	5.120%	$241.2819	$241.28	$241.30	$241.30
Purchase #4	$6.91	12.127%	$7.748	$7.75	$7.75	$7.70
Purchase #5	$130.79	13.668%	$148.6664	$148.67	$148.65	$148.70
Purchase #6	$230.38	13.626%	$261.7716	$261.77	$261.75	$261.80
Purchase #7	$160.72	12.402%	$180.6525	$180.65	$180.65	$180.70
7 purchase totals =	$1,007.57		$1,100.7268	$1,100.73	$1,100.70	$1,100.80