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	$151.82	9.598%	$166.3917	$166.39	$166.40	$166.40
Purchase #2	$218.50	5.233%	$229.9341	$229.93	$229.95	$229.90
Purchase #3	$202.41	10.184%	$223.0234	$223.02	$223.00	$223.00
Purchase #4	$131.80	5.641%	$139.2348	$139.23	$139.25	$139.20
Purchase #5	$209.46	6.518%	$223.1126	$223.11	$223.10	$223.10
Purchase #6	$135.51	9.814%	$148.809	$148.81	$148.80	$148.80
Purchase #7	$173.72	9.593%	$190.385	$190.39	$190.40	$190.40
7 purchase totals =	$1,223.22		$1,320.8906	$1,320.88	$1,320.90	$1,320.80