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	$207.47	6.462%	$220.8767	$220.88	$220.90	$220.90
Purchase #2	$12.47	8.127%	$13.4834	$13.48	$13.50	$13.50
Purchase #3	$192.56	10.297%	$212.3879	$212.39	$212.40	$212.40
Purchase #4	$243.45	6.774%	$259.9413	$259.94	$259.95	$259.90
Purchase #5	$143.41	11.841%	$160.3912	$160.39	$160.40	$160.40
Purchase #6	$165.64	5.548%	$174.8297	$174.83	$174.85	$174.80
Purchase #7	$76.40	11.834%	$85.4412	$85.44	$85.45	$85.40
7 purchase totals =	$1,041.40		$1,127.3514	$1,127.35	$1,127.45	$1,127.30