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	$77.55	13.853%	$88.293	$88.29	$88.30	$88.30
Purchase #2	$21.88	6.405%	$23.2814	$23.28	$23.30	$23.30
Purchase #3	$80.37	11.647%	$89.7307	$89.73	$89.75	$89.70
Purchase #4	$169.46	3.463%	$175.3284	$175.33	$175.35	$175.30
Purchase #5	$148.53	7.369%	$159.4752	$159.48	$159.50	$159.50
Purchase #6	$42.71	7.259%	$45.8103	$45.81	$45.80	$45.80
Purchase #7	$105.48	3.171%	$108.8248	$108.82	$108.80	$108.80
7 purchase totals =	$645.98		$690.7438	$690.74	$690.80	$690.70