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	$71.36	3.545%	$73.8897	$73.89	$73.90	$73.90
Purchase #2	$209.36	12.690%	$235.9278	$235.93	$235.95	$235.90
Purchase #3	$12.47	4.218%	$12.996	$13.00	$13.00	$13.00
Purchase #4	$245.60	13.553%	$278.8862	$278.89	$278.90	$278.90
Purchase #5	$118.90	10.222%	$131.054	$131.05	$131.05	$131.10
Purchase #6	$79.91	11.279%	$88.923	$88.92	$88.90	$88.90
Purchase #7	$172.73	9.330%	$188.8457	$188.85	$188.85	$188.80
7 purchase totals =	$910.33		$1,010.5224	$1,010.53	$1,010.55	$1,010.50