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	$87.81	5.778%	$92.8837	$92.88	$92.90	$92.90
Purchase #2	$220.80	9.551%	$241.8886	$241.89	$241.90	$241.90
Purchase #3	$181.41	10.519%	$200.4925	$200.49	$200.50	$200.50
Purchase #4	$56.36	5.123%	$59.2473	$59.25	$59.25	$59.20
Purchase #5	$161.35	5.809%	$170.7228	$170.72	$170.70	$170.70
Purchase #6	$78.34	9.859%	$86.0635	$86.06	$86.05	$86.10
Purchase #7	$120.74	7.524%	$129.8245	$129.82	$129.80	$129.80
7 purchase totals =	$906.81		$981.1229	$981.11	$981.10	$981.10