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	$85.75	6.700%	$91.4953	$91.50	$91.50	$91.50
Purchase #2	$90.76	6.597%	$96.7474	$96.75	$96.75	$96.70
Purchase #3	$209.66	12.815%	$236.5279	$236.53	$236.55	$236.50
Purchase #4	$32.83	6.181%	$34.8592	$34.86	$34.85	$34.90
Purchase #5	$185.55	12.705%	$209.1241	$209.12	$209.10	$209.10
Purchase #6	$144.73	4.399%	$151.0967	$151.10	$151.10	$151.10
Purchase #7	$173.68	10.776%	$192.3958	$192.40	$192.40	$192.40
7 purchase totals =	$922.96		$1,012.2464	$1,012.26	$1,012.25	$1,012.20