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	$168.88	9.727%	$185.307	$185.31	$185.30	$185.30
Purchase #2	$80.97	9.163%	$88.3893	$88.39	$88.40	$88.40
Purchase #3	$130.50	3.315%	$134.8261	$134.83	$134.85	$134.80
Purchase #4	$162.32	10.839%	$179.9139	$179.91	$179.90	$179.90
Purchase #5	$202.65	3.531%	$209.8056	$209.81	$209.80	$209.80
Purchase #6	$20.25	9.840%	$22.2426	$22.24	$22.25	$22.20
Purchase #7	$219.94	4.302%	$229.4018	$229.40	$229.40	$229.40
7 purchase totals =	$985.51		$1,049.8863	$1,049.89	$1,049.90	$1,049.80