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	$85.72	6.592%	$91.3707	$91.37	$91.35	$91.40
Purchase #2	$206.31	4.123%	$214.8162	$214.82	$214.80	$214.80
Purchase #3	$77.72	12.336%	$87.3075	$87.31	$87.30	$87.30
Purchase #4	$200.89	10.169%	$221.3185	$221.32	$221.30	$221.30
Purchase #5	$159.76	6.673%	$170.4208	$170.42	$170.40	$170.40
Purchase #6	$221.46	11.447%	$246.8105	$246.81	$246.80	$246.80
Purchase #7	$42.41	8.241%	$45.905	$45.91	$45.90	$45.90
7 purchase totals =	$994.27		$1,077.9492	$1,077.96	$1,077.85	$1,077.90