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	$139.30	4.512%	$145.5852	$145.59	$145.60	$145.60
Purchase #2	$69.95	4.281%	$72.9446	$72.94	$72.95	$72.90
Purchase #3	$38.63	11.450%	$43.0531	$43.05	$43.05	$43.10
Purchase #4	$162.32	10.718%	$179.7175	$179.72	$179.70	$179.70
Purchase #5	$239.75	4.225%	$249.8794	$249.88	$249.90	$249.90
Purchase #6	$59.88	12.756%	$67.5183	$67.52	$67.50	$67.50
Purchase #7	$205.59	8.127%	$222.2983	$222.30	$222.30	$222.30
7 purchase totals =	$915.42		$980.9964	$981.00	$981.00	$981.00