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	$46.87	7.549%	$50.4082	$50.41	$50.40	$50.40
Purchase #2	$113.77	12.660%	$128.1733	$128.17	$128.15	$128.20
Purchase #3	$167.81	13.376%	$190.2563	$190.26	$190.25	$190.30
Purchase #4	$188.97	6.834%	$201.8842	$201.88	$201.90	$201.90
Purchase #5	$118.26	4.263%	$123.3014	$123.30	$123.30	$123.30
Purchase #6	$48.69	13.642%	$55.3323	$55.33	$55.35	$55.30
Purchase #7	$56.25	8.620%	$61.0988	$61.10	$61.10	$61.10
7 purchase totals =	$740.62		$810.4545	$810.45	$810.45	$810.50