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	$86.82	6.586%	$92.538	$92.54	$92.55	$92.50
Purchase #2	$201.47	8.730%	$219.0583	$219.06	$219.05	$219.10
Purchase #3	$40.47	5.251%	$42.5951	$42.60	$42.60	$42.60
Purchase #4	$167.94	6.712%	$179.2121	$179.21	$179.20	$179.20
Purchase #5	$192.85	12.293%	$216.5571	$216.56	$216.55	$216.60
Purchase #6	$43.27	11.649%	$48.3105	$48.31	$48.30	$48.30
Purchase #7	$17.30	7.110%	$18.53	$18.53	$18.55	$18.50
7 purchase totals =	$750.12		$816.8011	$816.81	$816.80	$816.80