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	$99.64	9.180%	$108.787	$108.79	$108.80	$108.80
Purchase #2	$99.79	12.749%	$112.5122	$112.51	$112.50	$112.50
Purchase #3	$12.49	8.322%	$13.5294	$13.53	$13.55	$13.50
Purchase #4	$79.96	11.506%	$89.1602	$89.16	$89.15	$89.20
Purchase #5	$218.80	3.183%	$225.7644	$225.76	$225.75	$225.80
Purchase #6	$104.28	10.222%	$114.9395	$114.94	$114.95	$114.90
Purchase #7	$134.77	9.479%	$147.5448	$147.54	$147.55	$147.50
7 purchase totals =	$749.73		$812.2375	$812.23	$812.25	$812.20