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	$232.98	9.585%	$255.3111	$255.31	$255.30	$255.30
Purchase #2	$35.29	5.727%	$37.3111	$37.31	$37.30	$37.30
Purchase #3	$143.54	9.313%	$156.9079	$156.91	$156.90	$156.90
Purchase #4	$9.97	8.829%	$10.8503	$10.85	$10.85	$10.90
Purchase #5	$59.39	9.405%	$64.9756	$64.98	$65.00	$65.00
Purchase #6	$204.82	4.318%	$213.6641	$213.66	$213.65	$213.70
Purchase #7	$184.31	6.619%	$196.5095	$196.51	$196.50	$196.50
7 purchase totals =	$870.30		$935.5296	$935.53	$935.50	$935.60