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	$102.65	10.123%	$113.0413	$113.04	$113.05	$113.00
Purchase #2	$148.85	9.565%	$163.0875	$163.09	$163.10	$163.10
Purchase #3	$140.33	8.512%	$152.2749	$152.27	$152.25	$152.30
Purchase #4	$178.48	4.164%	$185.9119	$185.91	$185.90	$185.90
Purchase #5	$55.65	7.871%	$60.0302	$60.03	$60.05	$60.00
Purchase #6	$170.82	6.325%	$181.6244	$181.62	$181.60	$181.60
Purchase #7	$139.70	5.555%	$147.4603	$147.46	$147.45	$147.50
7 purchase totals =	$936.48		$1,003.4305	$1,003.42	$1,003.40	$1,003.40