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	$83.45	5.174%	$87.7677	$87.77	$87.75	$87.80
Purchase #2	$28.53	7.229%	$30.5924	$30.59	$30.60	$30.60
Purchase #3	$88.44	3.871%	$91.8635	$91.86	$91.85	$91.90
Purchase #4	$82.48	12.544%	$92.8263	$92.83	$92.85	$92.80
Purchase #5	$145.85	3.746%	$151.3135	$151.31	$151.30	$151.30
Purchase #6	$171.55	7.803%	$184.936	$184.94	$184.95	$184.90
Purchase #7	$6.73	10.435%	$7.4323	$7.43	$7.45	$7.40
7 purchase totals =	$607.03		$646.7317	$646.73	$646.75	$646.70