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	$10.89	9.483%	$11.9227	$11.92	$11.90	$11.90
Purchase #2	$56.43	10.570%	$62.3947	$62.39	$62.40	$62.40
Purchase #3	$149.87	11.811%	$167.5711	$167.57	$167.55	$167.60
Purchase #4	$87.96	5.279%	$92.6034	$92.60	$92.60	$92.60
Purchase #5	$33.66	11.695%	$37.5965	$37.60	$37.60	$37.60
Purchase #6	$197.27	13.280%	$223.4675	$223.47	$223.45	$223.50
Purchase #7	$207.88	7.774%	$224.0406	$224.04	$224.05	$224.00
7 purchase totals =	$743.96		$819.5965	$819.59	$819.55	$819.60