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	$30.74	3.523%	$31.823	$31.82	$31.80	$31.80
Purchase #2	$6.85	5.712%	$7.2413	$7.24	$7.25	$7.20
Purchase #3	$212.65	13.633%	$241.6406	$241.64	$241.65	$241.60
Purchase #4	$156.99	13.701%	$178.4992	$178.50	$178.50	$178.50
Purchase #5	$152.39	6.256%	$161.9235	$161.92	$161.90	$161.90
Purchase #6	$75.39	6.836%	$80.5437	$80.54	$80.55	$80.50
Purchase #7	$79.65	13.712%	$90.5716	$90.57	$90.55	$90.60
7 purchase totals =	$714.66		$792.2429	$792.23	$792.20	$792.10