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	$55.65	6.621%	$59.3346	$59.33	$59.35	$59.30
Purchase #2	$70.50	12.225%	$79.1186	$79.12	$79.10	$79.10
Purchase #3	$159.87	5.465%	$168.6069	$168.61	$168.60	$168.60
Purchase #4	$93.84	7.107%	$100.5092	$100.51	$100.50	$100.50
Purchase #5	$67.57	13.866%	$76.9393	$76.94	$76.95	$76.90
Purchase #6	$82.34	4.490%	$86.0371	$86.04	$86.05	$86.00
Purchase #7	$163.40	5.262%	$171.9981	$172.00	$172.00	$172.00
7 purchase totals =	$693.17		$742.5438	$742.55	$742.55	$742.40