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	$124.50	10.491%	$137.5613	$137.56	$137.55	$137.60
Purchase #2	$60.51	11.551%	$67.4995	$67.50	$67.50	$67.50
Purchase #3	$83.36	6.674%	$88.9234	$88.92	$88.90	$88.90
Purchase #4	$11.63	11.796%	$13.0019	$13.00	$13.00	$13.00
Purchase #5	$68.67	3.595%	$71.1387	$71.14	$71.15	$71.10
Purchase #6	$95.53	5.385%	$100.6743	$100.67	$100.65	$100.70
Purchase #7	$30.69	10.148%	$33.8044	$33.80	$33.80	$33.80
7 purchase totals =	$474.89		$512.6035	$512.59	$512.55	$512.60