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	$66.42	9.749%	$72.8953	$72.90	$72.90	$72.90
Purchase #2	$35.96	4.570%	$37.6034	$37.60	$37.60	$37.60
Purchase #3	$225.44	5.733%	$238.3645	$238.36	$238.35	$238.40
Purchase #4	$36.80	12.707%	$41.4762	$41.48	$41.50	$41.50
Purchase #5	$199.61	5.417%	$210.4229	$210.42	$210.40	$210.40
Purchase #6	$118.31	4.128%	$123.1938	$123.19	$123.20	$123.20
Purchase #7	$42.70	5.862%	$45.2031	$45.20	$45.20	$45.20
7 purchase totals =	$725.24		$769.1592	$769.15	$769.15	$769.20