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	$200.97	11.866%	$224.8171	$224.82	$224.80	$224.80
Purchase #2	$89.42	13.116%	$101.1483	$101.15	$101.15	$101.10
Purchase #3	$25.31	12.269%	$28.4153	$28.42	$28.40	$28.40
Purchase #4	$11.32	10.411%	$12.4985	$12.50	$12.50	$12.50
Purchase #5	$96.83	5.481%	$102.1373	$102.14	$102.15	$102.10
Purchase #6	$60.80	11.688%	$67.9063	$67.91	$67.90	$67.90
Purchase #7	$55.63	4.463%	$58.1128	$58.11	$58.10	$58.10
7 purchase totals =	$540.28		$595.0356	$595.05	$595.00	$594.90