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	$155.71	9.854%	$171.0537	$171.05	$171.05	$171.10
Purchase #2	$203.79	6.297%	$216.6227	$216.62	$216.60	$216.60
Purchase #3	$225.60	4.529%	$235.8174	$235.82	$235.80	$235.80
Purchase #4	$223.64	9.816%	$245.5925	$245.59	$245.60	$245.60
Purchase #5	$90.53	10.457%	$99.9967	$100.00	$100.00	$100.00
Purchase #6	$139.83	3.668%	$144.959	$144.96	$144.95	$145.00
Purchase #7	$34.49	7.476%	$37.0685	$37.07	$37.05	$37.10
7 purchase totals =	$1,073.59		$1,151.1105	$1,151.11	$1,151.05	$1,151.20