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	$16.70	10.652%	$18.4789	$18.48	$18.50	$18.50
Purchase #2	$59.63	3.144%	$61.5048	$61.50	$61.50	$61.50
Purchase #3	$30.30	7.172%	$32.4731	$32.47	$32.45	$32.50
Purchase #4	$87.35	3.826%	$90.692	$90.69	$90.70	$90.70
Purchase #5	$51.58	4.231%	$53.7623	$53.76	$53.75	$53.80
Purchase #6	$59.92	12.294%	$67.2866	$67.29	$67.30	$67.30
Purchase #7	$70.83	3.552%	$73.3459	$73.35	$73.35	$73.30
7 purchase totals =	$376.31		$397.5436	$397.54	$397.55	$397.60