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	$79.90	5.607%	$84.38	$84.38	$84.40	$84.40
Purchase #2	$67.90	5.789%	$71.8307	$71.83	$71.85	$71.80
Purchase #3	$106.86	10.191%	$117.7501	$117.75	$117.75	$117.80
Purchase #4	$69.98	12.179%	$78.5029	$78.50	$78.50	$78.50
Purchase #5	$40.31	13.830%	$45.8849	$45.88	$45.90	$45.90
Purchase #6	$149.73	3.198%	$154.5184	$154.52	$154.50	$154.50
Purchase #7	$5.43	4.574%	$5.6784	$5.68	$5.70	$5.70
7 purchase totals =	$520.11		$558.5454	$558.54	$558.60	$558.60