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	$51.91	3.120%	$53.5296	$53.53	$53.55	$53.50
Purchase #2	$101.54	8.776%	$110.4512	$110.45	$110.45	$110.50
Purchase #3	$168.80	12.582%	$190.0384	$190.04	$190.05	$190.00
Purchase #4	$33.43	12.332%	$37.5526	$37.55	$37.55	$37.60
Purchase #5	$240.52	3.841%	$249.7584	$249.76	$249.75	$249.80
Purchase #6	$123.25	5.538%	$130.0756	$130.08	$130.10	$130.10
Purchase #7	$29.45	13.670%	$33.4758	$33.48	$33.50	$33.50
7 purchase totals =	$748.90		$804.8816	$804.89	$804.95	$805.00