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	$135.33	12.343%	$152.0338	$152.03	$152.05	$152.00
Purchase #2	$76.33	12.429%	$85.8171	$85.82	$85.80	$85.80
Purchase #3	$92.69	8.645%	$100.7031	$100.70	$100.70	$100.70
Purchase #4	$34.71	4.571%	$36.2966	$36.30	$36.30	$36.30
Purchase #5	$75.68	5.817%	$80.0823	$80.08	$80.10	$80.10
Purchase #6	$127.54	7.747%	$137.4205	$137.42	$137.40	$137.40
Purchase #7	$100.75	7.622%	$108.4292	$108.43	$108.45	$108.40
7 purchase totals =	$643.03		$700.7826	$700.78	$700.80	$700.70