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	$109.61	12.488%	$123.2981	$123.30	$123.30	$123.30
Purchase #2	$103.56	7.606%	$111.4368	$111.44	$111.45	$111.40
Purchase #3	$204.85	12.764%	$230.9971	$231.00	$231.00	$231.00
Purchase #4	$80.27	12.409%	$90.2307	$90.23	$90.25	$90.20
Purchase #5	$78.54	8.204%	$84.9834	$84.98	$85.00	$85.00
Purchase #6	$25.52	12.272%	$28.6518	$28.65	$28.65	$28.70
Purchase #7	$79.42	3.338%	$82.071	$82.07	$82.05	$82.10
7 purchase totals =	$681.77		$751.6689	$751.67	$751.70	$751.70