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	$7.51	12.441%	$8.4443	$8.44	$8.45	$8.40
Purchase #2	$81.74	9.736%	$89.6982	$89.70	$89.70	$89.70
Purchase #3	$99.83	13.514%	$113.321	$113.32	$113.30	$113.30
Purchase #4	$161.67	10.362%	$178.4222	$178.42	$178.40	$178.40
Purchase #5	$83.32	3.241%	$86.0204	$86.02	$86.00	$86.00
Purchase #6	$207.63	7.588%	$223.385	$223.39	$223.40	$223.40
Purchase #7	$130.78	11.858%	$146.2879	$146.29	$146.30	$146.30
7 purchase totals =	$772.48		$845.5790	$845.58	$845.55	$845.50