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	$97.67	4.325%	$101.8942	$101.89	$101.90	$101.90
Purchase #2	$232.65	7.517%	$250.1383	$250.14	$250.15	$250.10
Purchase #3	$94.45	11.657%	$105.46	$105.46	$105.45	$105.50
Purchase #4	$80.39	12.568%	$90.4934	$90.49	$90.50	$90.50
Purchase #5	$81.81	4.441%	$85.4432	$85.44	$85.45	$85.40
Purchase #6	$144.79	9.145%	$158.031	$158.03	$158.05	$158.00
Purchase #7	$7.53	13.607%	$8.5546	$8.55	$8.55	$8.60
7 purchase totals =	$739.29		$800.0147	$800.00	$800.05	$800.00