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	$37.49	10.699%	$41.5011	$41.50	$41.50	$41.50
Purchase #2	$240.30	13.759%	$273.3629	$273.36	$273.35	$273.40
Purchase #3	$212.73	10.151%	$234.3242	$234.32	$234.30	$234.30
Purchase #4	$154.72	9.134%	$168.8521	$168.85	$168.85	$168.90
Purchase #5	$137.29	12.294%	$154.1684	$154.17	$154.15	$154.20
Purchase #6	$216.76	7.200%	$232.3667	$232.37	$232.35	$232.40
Purchase #7	$150.37	5.631%	$158.8373	$158.84	$158.85	$158.80
7 purchase totals =	$1,149.66		$1,263.4127	$1,263.41	$1,263.35	$1,263.50