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	$124.42	9.698%	$136.4863	$136.49	$136.50	$136.50
Purchase #2	$91.54	9.477%	$100.2152	$100.22	$100.20	$100.20
Purchase #3	$85.69	3.445%	$88.642	$88.64	$88.65	$88.60
Purchase #4	$90.41	4.212%	$94.2181	$94.22	$94.20	$94.20
Purchase #5	$249.71	8.778%	$271.6295	$271.63	$271.65	$271.60
Purchase #6	$62.31	13.769%	$70.8895	$70.89	$70.90	$70.90
Purchase #7	$249.37	3.718%	$258.6416	$258.64	$258.65	$258.60
7 purchase totals =	$953.45		$1,020.7222	$1,020.73	$1,020.75	$1,020.60