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	$94.54	7.171%	$101.3195	$101.32	$101.30	$101.30
Purchase #2	$86.51	4.842%	$90.6988	$90.70	$90.70	$90.70
Purchase #3	$210.49	9.235%	$229.9288	$229.93	$229.95	$229.90
Purchase #4	$69.65	12.715%	$78.506	$78.51	$78.50	$78.50
Purchase #5	$140.96	3.194%	$145.4623	$145.46	$145.45	$145.50
Purchase #6	$103.74	9.687%	$113.7893	$113.79	$113.80	$113.80
Purchase #7	$27.79	8.140%	$30.0521	$30.05	$30.05	$30.10
7 purchase totals =	$733.68		$789.7568	$789.76	$789.75	$789.80