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	$96.60	3.738%	$100.2109	$100.21	$100.20	$100.20
Purchase #2	$125.67	11.281%	$139.8468	$139.85	$139.85	$139.80
Purchase #3	$20.51	10.604%	$22.6849	$22.68	$22.70	$22.70
Purchase #4	$19.62	8.196%	$21.2281	$21.23	$21.25	$21.20
Purchase #5	$84.78	5.570%	$89.5022	$89.50	$89.50	$89.50
Purchase #6	$59.48	4.546%	$62.184	$62.18	$62.20	$62.20
Purchase #7	$94.88	4.360%	$99.0168	$99.02	$99.00	$99.00
7 purchase totals =	$501.54		$534.6737	$534.67	$534.70	$534.60