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	$155.50	11.110%	$172.7761	$172.78	$172.80	$172.80
Purchase #2	$78.42	13.553%	$89.0483	$89.05	$89.05	$89.00
Purchase #3	$223.75	12.204%	$251.0565	$251.06	$251.05	$251.10
Purchase #4	$84.85	5.297%	$89.3445	$89.34	$89.35	$89.30
Purchase #5	$106.67	12.471%	$119.9728	$119.97	$119.95	$120.00
Purchase #6	$87.84	4.690%	$91.9597	$91.96	$91.95	$92.00
Purchase #7	$200.28	6.805%	$213.9091	$213.91	$213.90	$213.90
7 purchase totals =	$937.31		$1,028.0670	$1,028.07	$1,028.05	$1,028.10