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	$78.39	5.623%	$82.7979	$82.80	$82.80	$82.80
Purchase #2	$174.61	9.471%	$191.1473	$191.15	$191.15	$191.10
Purchase #3	$34.82	12.514%	$39.1774	$39.18	$39.20	$39.20
Purchase #4	$130.25	11.209%	$144.8497	$144.85	$144.85	$144.80
Purchase #5	$84.32	5.756%	$89.1735	$89.17	$89.15	$89.20
Purchase #6	$26.71	10.772%	$29.5872	$29.59	$29.60	$29.60
Purchase #7	$170.65	9.457%	$186.7884	$186.79	$186.80	$186.80
7 purchase totals =	$699.75		$763.5214	$763.53	$763.55	$763.50