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	$77.76	3.181%	$80.2335	$80.23	$80.25	$80.20
Purchase #2	$28.71	4.287%	$29.9408	$29.94	$29.95	$29.90
Purchase #3	$20.61	6.798%	$22.0111	$22.01	$22.00	$22.00
Purchase #4	$216.42	4.348%	$225.8299	$225.83	$225.85	$225.80
Purchase #5	$151.36	5.550%	$159.7605	$159.76	$159.75	$159.80
Purchase #6	$36.72	11.341%	$40.8844	$40.88	$40.90	$40.90
Purchase #7	$207.72	7.463%	$223.2221	$223.22	$223.20	$223.20
7 purchase totals =	$739.30		$781.8823	$781.87	$781.90	$781.80