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	$170.92	3.810%	$177.4321	$177.43	$177.45	$177.40
Purchase #2	$70.31	7.139%	$75.3294	$75.33	$75.35	$75.30
Purchase #3	$88.25	4.622%	$92.3289	$92.33	$92.35	$92.30
Purchase #4	$80.52	12.518%	$90.5995	$90.60	$90.60	$90.60
Purchase #5	$200.56	4.655%	$209.8961	$209.90	$209.90	$209.90
Purchase #6	$197.56	11.539%	$220.3564	$220.36	$220.35	$220.40
Purchase #7	$41.64	4.490%	$43.5096	$43.51	$43.50	$43.50
7 purchase totals =	$849.76		$909.4520	$909.46	$909.50	$909.40