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	$80.46	12.490%	$90.5095	$90.51	$90.50	$90.50
Purchase #2	$160.39	7.759%	$172.8347	$172.83	$172.85	$172.80
Purchase #3	$121.32	3.411%	$125.4582	$125.46	$125.45	$125.50
Purchase #4	$110.28	11.293%	$122.7339	$122.73	$122.75	$122.70
Purchase #5	$148.98	11.215%	$165.6881	$165.69	$165.70	$165.70
Purchase #6	$213.44	9.313%	$233.3177	$233.32	$233.30	$233.30
Purchase #7	$159.81	3.855%	$165.9707	$165.97	$165.95	$166.00
7 purchase totals =	$994.68		$1,076.5128	$1,076.51	$1,076.50	$1,076.50