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	$232.83	9.245%	$254.3551	$254.36	$254.35	$254.40
Purchase #2	$223.51	10.462%	$246.8936	$246.89	$246.90	$246.90
Purchase #3	$54.87	8.394%	$59.4758	$59.48	$59.50	$59.50
Purchase #4	$203.83	7.443%	$219.0011	$219.00	$219.00	$219.00
Purchase #5	$52.72	12.516%	$59.3184	$59.32	$59.30	$59.30
Purchase #6	$136.75	4.471%	$142.8641	$142.86	$142.85	$142.90
Purchase #7	$182.88	13.255%	$207.1207	$207.12	$207.10	$207.10
7 purchase totals =	$1,087.39		$1,189.0288	$1,189.03	$1,189.00	$1,189.10