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	$75.40	8.578%	$81.8678	$81.87	$81.85	$81.90
Purchase #2	$227.42	3.303%	$234.9317	$234.93	$234.95	$234.90
Purchase #3	$32.95	8.807%	$35.8519	$35.85	$35.85	$35.90
Purchase #4	$27.47	5.385%	$28.9493	$28.95	$28.95	$28.90
Purchase #5	$11.82	3.771%	$12.2657	$12.27	$12.25	$12.30
Purchase #6	$90.88	9.271%	$99.3055	$99.31	$99.30	$99.30
Purchase #7	$52.89	13.732%	$60.1529	$60.15	$60.15	$60.20
7 purchase totals =	$518.83		$553.3248	$553.33	$553.30	$553.40