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	$217.73	12.231%	$244.3606	$244.36	$244.35	$244.40
Purchase #2	$245.89	13.612%	$279.3605	$279.36	$279.35	$279.40
Purchase #3	$156.50	9.386%	$171.1891	$171.19	$171.20	$171.20
Purchase #4	$23.38	6.833%	$24.9776	$24.98	$25.00	$25.00
Purchase #5	$127.80	7.811%	$137.7825	$137.78	$137.80	$137.80
Purchase #6	$113.71	12.281%	$127.6747	$127.67	$127.65	$127.70
Purchase #7	$144.29	8.656%	$156.7797	$156.78	$156.80	$156.80
7 purchase totals =	$1,029.30		$1,142.1247	$1,142.12	$1,142.15	$1,142.30