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	$98.61	8.425%	$106.9179	$106.92	$106.90	$106.90
Purchase #2	$91.53	7.184%	$98.1055	$98.11	$98.10	$98.10
Purchase #3	$127.54	9.307%	$139.4101	$139.41	$139.40	$139.40
Purchase #4	$223.61	8.380%	$242.3485	$242.35	$242.35	$242.30
Purchase #5	$187.54	10.186%	$206.6428	$206.64	$206.65	$206.60
Purchase #6	$211.95	12.660%	$238.7829	$238.78	$238.80	$238.80
Purchase #7	$149.98	12.467%	$168.678	$168.68	$168.70	$168.70
7 purchase totals =	$1,090.76		$1,200.8857	$1,200.89	$1,200.90	$1,200.80