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	$152.36	10.846%	$168.885	$168.89	$168.90	$168.90
Purchase #2	$193.46	13.653%	$219.8731	$219.87	$219.85	$219.90
Purchase #3	$98.71	6.380%	$105.0077	$105.01	$105.00	$105.00
Purchase #4	$133.64	7.639%	$143.8488	$143.85	$143.85	$143.80
Purchase #5	$232.67	4.205%	$242.4538	$242.45	$242.45	$242.50
Purchase #6	$118.55	5.543%	$125.1212	$125.12	$125.10	$125.10
Purchase #7	$158.94	10.651%	$175.8687	$175.87	$175.85	$175.90
7 purchase totals =	$1,088.33		$1,181.0583	$1,181.06	$1,181.00	$1,181.10