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	$144.83	4.133%	$150.8158	$150.82	$150.80	$150.80
Purchase #2	$93.54	12.690%	$105.4102	$105.41	$105.40	$105.40
Purchase #3	$82.87	5.163%	$87.1486	$87.15	$87.15	$87.10
Purchase #4	$148.50	5.163%	$156.1671	$156.17	$156.15	$156.20
Purchase #5	$195.86	11.672%	$218.7208	$218.72	$218.70	$218.70
Purchase #6	$86.91	3.849%	$90.2552	$90.26	$90.25	$90.30
Purchase #7	$97.90	12.803%	$110.4341	$110.43	$110.45	$110.40
7 purchase totals =	$850.41		$918.9518	$918.96	$918.90	$918.90