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	$167.71	12.717%	$189.0377	$189.04	$189.05	$189.00
Purchase #2	$73.58	9.237%	$80.3766	$80.38	$80.40	$80.40
Purchase #3	$238.83	5.423%	$251.7818	$251.78	$251.80	$251.80
Purchase #4	$45.34	7.500%	$48.7405	$48.74	$48.75	$48.70
Purchase #5	$98.64	7.531%	$106.0686	$106.07	$106.05	$106.10
Purchase #6	$41.35	3.708%	$42.8833	$42.88	$42.90	$42.90
Purchase #7	$40.73	12.668%	$45.8897	$45.89	$45.90	$45.90
7 purchase totals =	$706.18		$764.7782	$764.78	$764.85	$764.80