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	$136.67	13.764%	$155.4813	$155.48	$155.50	$155.50
Purchase #2	$74.56	7.475%	$80.1334	$80.13	$80.15	$80.10
Purchase #3	$108.54	6.496%	$115.5908	$115.59	$115.60	$115.60
Purchase #4	$64.94	10.822%	$71.9678	$71.97	$71.95	$72.00
Purchase #5	$207.34	6.141%	$220.0727	$220.07	$220.05	$220.10
Purchase #6	$111.61	8.139%	$120.6939	$120.69	$120.70	$120.70
Purchase #7	$18.64	10.121%	$20.5266	$20.53	$20.55	$20.50
7 purchase totals =	$722.30		$784.4665	$784.46	$784.50	$784.50