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	$140.31	13.400%	$159.1115	$159.11	$159.10	$159.10
Purchase #2	$37.30	13.734%	$42.4228	$42.42	$42.40	$42.40
Purchase #3	$67.38	3.117%	$69.4802	$69.48	$69.50	$69.50
Purchase #4	$38.43	11.514%	$42.8548	$42.85	$42.85	$42.90
Purchase #5	$30.62	3.826%	$31.7915	$31.79	$31.80	$31.80
Purchase #6	$22.62	4.573%	$23.6544	$23.65	$23.65	$23.70
Purchase #7	$250.88	4.243%	$261.5248	$261.52	$261.50	$261.50
7 purchase totals =	$587.54		$630.8400	$630.82	$630.80	$630.90