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	$5.50	4.777%	$5.7627	$5.76	$5.75	$5.80
Purchase #2	$243.94	10.228%	$268.8902	$268.89	$268.90	$268.90
Purchase #3	$55.62	9.142%	$60.7048	$60.70	$60.70	$60.70
Purchase #4	$76.99	11.541%	$85.8754	$85.88	$85.90	$85.90
Purchase #5	$86.82	3.759%	$90.0836	$90.08	$90.10	$90.10
Purchase #6	$106.42	5.166%	$111.9177	$111.92	$111.90	$111.90
Purchase #7	$23.72	10.118%	$26.12	$26.12	$26.10	$26.10
7 purchase totals =	$599.01		$649.3544	$649.35	$649.35	$649.40