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	$191.37	11.607%	$213.5823	$213.58	$213.60	$213.60
Purchase #2	$159.79	3.198%	$164.9001	$164.90	$164.90	$164.90
Purchase #3	$155.98	10.178%	$171.8556	$171.86	$171.85	$171.90
Purchase #4	$129.94	8.258%	$140.6704	$140.67	$140.65	$140.70
Purchase #5	$61.49	11.390%	$68.4937	$68.49	$68.50	$68.50
Purchase #6	$24.34	13.333%	$27.5853	$27.59	$27.60	$27.60
Purchase #7	$59.89	12.560%	$67.4122	$67.41	$67.40	$67.40
7 purchase totals =	$782.80		$854.4996	$854.50	$854.50	$854.60