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	$247.72	9.498%	$271.2484	$271.25	$271.25	$271.20
Purchase #2	$179.63	11.848%	$200.9126	$200.91	$200.90	$200.90
Purchase #3	$39.65	7.459%	$42.6075	$42.61	$42.60	$42.60
Purchase #4	$85.39	3.789%	$88.6254	$88.63	$88.65	$88.60
Purchase #5	$104.97	10.388%	$115.8743	$115.87	$115.85	$115.90
Purchase #6	$20.48	3.690%	$21.2357	$21.24	$21.25	$21.20
Purchase #7	$163.72	11.801%	$183.0406	$183.04	$183.05	$183.00
7 purchase totals =	$841.56		$923.5445	$923.55	$923.55	$923.40