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	$110.89	9.212%	$121.1052	$121.11	$121.10	$121.10
Purchase #2	$87.63	7.144%	$93.8903	$93.89	$93.90	$93.90
Purchase #3	$114.42	11.386%	$127.4479	$127.45	$127.45	$127.40
Purchase #4	$39.62	6.354%	$42.1375	$42.14	$42.15	$42.10
Purchase #5	$196.68	11.586%	$219.4673	$219.47	$219.45	$219.50
Purchase #6	$138.50	6.516%	$147.5247	$147.52	$147.50	$147.50
Purchase #7	$31.52	10.524%	$34.8372	$34.84	$34.85	$34.80
7 purchase totals =	$719.26		$786.4101	$786.42	$786.40	$786.30