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	$135.44	11.415%	$150.9005	$150.90	$150.90	$150.90
Purchase #2	$139.38	8.543%	$151.2872	$151.29	$151.30	$151.30
Purchase #3	$164.51	3.685%	$170.5722	$170.57	$170.55	$170.60
Purchase #4	$116.72	8.804%	$126.996	$127.00	$127.00	$127.00
Purchase #5	$86.27	6.249%	$91.661	$91.66	$91.65	$91.70
Purchase #6	$6.87	13.279%	$7.7823	$7.78	$7.80	$7.80
Purchase #7	$62.88	13.290%	$71.2368	$71.24	$71.25	$71.20
7 purchase totals =	$712.07		$770.4360	$770.44	$770.45	$770.50