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	$92.69	7.720%	$99.8457	$99.85	$99.85	$99.80
Purchase #2	$109.61	12.133%	$122.909	$122.91	$122.90	$122.90
Purchase #3	$221.43	8.753%	$240.8118	$240.81	$240.80	$240.80
Purchase #4	$170.75	11.190%	$189.8569	$189.86	$189.85	$189.90
Purchase #5	$82.91	8.666%	$90.095	$90.10	$90.10	$90.10
Purchase #6	$98.39	7.146%	$105.4209	$105.42	$105.40	$105.40
Purchase #7	$85.90	3.278%	$88.7158	$88.72	$88.70	$88.70
7 purchase totals =	$861.68		$937.6551	$937.67	$937.60	$937.60