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	$105.99	13.467%	$120.2637	$120.26	$120.25	$120.30
Purchase #2	$50.98	8.628%	$55.3786	$55.38	$55.40	$55.40
Purchase #3	$119.61	4.650%	$125.1719	$125.17	$125.15	$125.20
Purchase #4	$25.50	8.524%	$27.6736	$27.67	$27.65	$27.70
Purchase #5	$38.37	5.765%	$40.582	$40.58	$40.60	$40.60
Purchase #6	$160.29	7.562%	$172.4111	$172.41	$172.40	$172.40
Purchase #7	$94.87	5.250%	$99.8507	$99.85	$99.85	$99.90
7 purchase totals =	$595.61		$641.3316	$641.32	$641.30	$641.50