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	$56.90	3.860%	$59.0963	$59.10	$59.10	$59.10
Purchase #2	$23.46	10.440%	$25.9092	$25.91	$25.90	$25.90
Purchase #3	$84.56	4.482%	$88.35	$88.35	$88.35	$88.40
Purchase #4	$142.52	6.480%	$151.7553	$151.76	$151.75	$151.80
Purchase #5	$25.84	8.466%	$28.0276	$28.03	$28.05	$28.00
Purchase #6	$156.46	12.456%	$175.9487	$175.95	$175.95	$175.90
Purchase #7	$209.45	9.729%	$229.8274	$229.83	$229.85	$229.80
7 purchase totals =	$699.19		$758.9145	$758.93	$758.95	$758.90