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	$55.29	8.307%	$59.8829	$59.88	$59.90	$59.90
Purchase #2	$73.64	7.141%	$78.8986	$78.90	$78.90	$78.90
Purchase #3	$157.79	9.487%	$172.7595	$172.76	$172.75	$172.80
Purchase #4	$75.80	13.449%	$85.9943	$85.99	$86.00	$86.00
Purchase #5	$85.34	11.592%	$95.2326	$95.23	$95.25	$95.20
Purchase #6	$238.43	11.790%	$266.5409	$266.54	$266.55	$266.50
Purchase #7	$207.56	6.346%	$220.7318	$220.73	$220.75	$220.70
7 purchase totals =	$893.85		$980.0406	$980.03	$980.10	$980.00