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	$171.94	6.618%	$183.319	$183.32	$183.30	$183.30
Purchase #2	$164.77	12.655%	$185.6216	$185.62	$185.60	$185.60
Purchase #3	$222.43	10.121%	$244.9421	$244.94	$244.95	$244.90
Purchase #4	$137.79	10.398%	$152.1174	$152.12	$152.10	$152.10
Purchase #5	$68.47	10.611%	$75.7354	$75.74	$75.75	$75.70
Purchase #6	$113.31	9.164%	$123.6937	$123.69	$123.70	$123.70
Purchase #7	$221.48	6.204%	$235.2206	$235.22	$235.20	$235.20
7 purchase totals =	$1,100.19		$1,200.6498	$1,200.65	$1,200.60	$1,200.50