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	$241.35	5.498%	$254.6194	$254.62	$254.60	$254.60
Purchase #2	$191.82	11.118%	$213.1465	$213.15	$213.15	$213.10
Purchase #3	$145.97	3.295%	$150.7797	$150.78	$150.80	$150.80
Purchase #4	$84.54	6.647%	$90.1594	$90.16	$90.15	$90.20
Purchase #5	$19.69	11.870%	$22.0272	$22.03	$22.05	$22.00
Purchase #6	$41.50	10.495%	$45.8554	$45.86	$45.85	$45.90
Purchase #7	$30.72	5.111%	$32.2901	$32.29	$32.30	$32.30
7 purchase totals =	$755.59		$808.8777	$808.89	$808.90	$808.90