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	$26.86	3.697%	$27.853	$27.85	$27.85	$27.90
Purchase #2	$173.25	3.821%	$179.8699	$179.87	$179.85	$179.90
Purchase #3	$97.43	4.329%	$101.6477	$101.65	$101.65	$101.60
Purchase #4	$226.51	3.202%	$233.7629	$233.76	$233.75	$233.80
Purchase #5	$179.40	3.484%	$185.6503	$185.65	$185.65	$185.70
Purchase #6	$43.83	4.631%	$45.8598	$45.86	$45.85	$45.90
Purchase #7	$209.52	3.483%	$216.8176	$216.82	$216.80	$216.80
7 purchase totals =	$956.80		$991.4612	$991.46	$991.40	$991.60