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	$154.74	7.465%	$166.2913	$166.29	$166.30	$166.30
Purchase #2	$104.87	3.539%	$108.5813	$108.58	$108.60	$108.60
Purchase #3	$152.62	5.216%	$160.5807	$160.58	$160.60	$160.60
Purchase #4	$174.93	12.563%	$196.9065	$196.91	$196.90	$196.90
Purchase #5	$194.81	12.214%	$218.6041	$218.60	$218.60	$218.60
Purchase #6	$49.73	13.761%	$56.5733	$56.57	$56.55	$56.60
Purchase #7	$118.70	10.410%	$131.0567	$131.06	$131.05	$131.10
7 purchase totals =	$950.40		$1,038.5939	$1,038.59	$1,038.60	$1,038.70