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	$90.56	11.658%	$101.1175	$101.12	$101.10	$101.10
Purchase #2	$155.69	12.474%	$175.1108	$175.11	$175.10	$175.10
Purchase #3	$35.80	8.281%	$38.7646	$38.76	$38.75	$38.80
Purchase #4	$74.88	10.146%	$82.4773	$82.48	$82.50	$82.50
Purchase #5	$111.43	9.370%	$121.871	$121.87	$121.85	$121.90
Purchase #6	$199.26	12.108%	$223.3864	$223.39	$223.40	$223.40
Purchase #7	$59.39	9.589%	$65.0849	$65.08	$65.10	$65.10
7 purchase totals =	$727.01		$807.8125	$807.81	$807.80	$807.90