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	$237.38	7.304%	$254.7182	$254.72	$254.70	$254.70
Purchase #2	$177.40	10.574%	$196.1583	$196.16	$196.15	$196.20
Purchase #3	$26.89	12.697%	$30.3042	$30.30	$30.30	$30.30
Purchase #4	$223.89	9.592%	$245.3655	$245.37	$245.35	$245.40
Purchase #5	$145.69	4.542%	$152.3072	$152.31	$152.30	$152.30
Purchase #6	$180.91	6.596%	$192.8428	$192.84	$192.85	$192.80
Purchase #7	$143.67	8.806%	$156.3216	$156.32	$156.30	$156.30
7 purchase totals =	$1,135.83		$1,228.0178	$1,228.02	$1,227.95	$1,228.00