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	$38.39	6.367%	$40.8343	$40.83	$40.85	$40.80
Purchase #2	$73.80	3.745%	$76.5638	$76.56	$76.55	$76.60
Purchase #3	$235.48	4.574%	$246.2509	$246.25	$246.25	$246.30
Purchase #4	$173.75	7.434%	$186.6666	$186.67	$186.65	$186.70
Purchase #5	$96.26	9.413%	$105.321	$105.32	$105.30	$105.30
Purchase #6	$79.76	11.293%	$88.7673	$88.77	$88.75	$88.80
Purchase #7	$243.89	11.824%	$272.7276	$272.73	$272.75	$272.70
7 purchase totals =	$941.33		$1,017.1315	$1,017.13	$1,017.10	$1,017.20