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	$155.88	7.507%	$167.5819	$167.58	$167.60	$167.60
Purchase #2	$245.70	8.597%	$266.8228	$266.82	$266.80	$266.80
Purchase #3	$225.46	12.427%	$253.4779	$253.48	$253.50	$253.50
Purchase #4	$161.49	12.240%	$181.2564	$181.26	$181.25	$181.30
Purchase #5	$87.38	8.222%	$94.5644	$94.56	$94.55	$94.60
Purchase #6	$168.29	3.553%	$174.2693	$174.27	$174.25	$174.30
Purchase #7	$144.97	12.262%	$162.7462	$162.75	$162.75	$162.70
7 purchase totals =	$1,189.17		$1,300.7189	$1,300.72	$1,300.70	$1,300.80