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	$186.43	3.424%	$192.8134	$192.81	$192.80	$192.80
Purchase #2	$81.76	12.686%	$92.1321	$92.13	$92.15	$92.10
Purchase #3	$140.29	4.510%	$146.6171	$146.62	$146.60	$146.60
Purchase #4	$248.42	6.695%	$265.0517	$265.05	$265.05	$265.10
Purchase #5	$96.75	13.460%	$109.7726	$109.77	$109.75	$109.80
Purchase #6	$179.37	6.178%	$190.4515	$190.45	$190.45	$190.50
Purchase #7	$139.57	7.683%	$150.2932	$150.29	$150.30	$150.30
7 purchase totals =	$1,072.59		$1,147.1316	$1,147.12	$1,147.10	$1,147.20