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	$70.79	11.574%	$78.9832	$78.98	$79.00	$79.00
Purchase #2	$49.66	13.868%	$56.5468	$56.55	$56.55	$56.50
Purchase #3	$73.74	6.337%	$78.4129	$78.41	$78.40	$78.40
Purchase #4	$243.62	13.245%	$275.8875	$275.89	$275.90	$275.90
Purchase #5	$165.44	4.424%	$172.7591	$172.76	$172.75	$172.80
Purchase #6	$90.96	9.823%	$99.895	$99.90	$99.90	$99.90
Purchase #7	$28.50	11.874%	$31.8841	$31.88	$31.90	$31.90
7 purchase totals =	$722.71		$794.3686	$794.37	$794.40	$794.40