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	$185.72	6.760%	$198.2747	$198.27	$198.25	$198.30
Purchase #2	$34.84	11.489%	$38.8428	$38.84	$38.85	$38.80
Purchase #3	$249.95	8.653%	$271.5782	$271.58	$271.60	$271.60
Purchase #4	$228.60	9.700%	$250.7742	$250.77	$250.75	$250.80
Purchase #5	$38.86	9.827%	$42.6788	$42.68	$42.70	$42.70
Purchase #6	$161.32	6.357%	$171.5751	$171.58	$171.60	$171.60
Purchase #7	$158.37	3.810%	$164.4039	$164.40	$164.40	$164.40
7 purchase totals =	$1,057.66		$1,138.1277	$1,138.12	$1,138.15	$1,138.20