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	$215.77	6.506%	$229.808	$229.81	$229.80	$229.80
Purchase #2	$81.80	9.556%	$89.6168	$89.62	$89.60	$89.60
Purchase #3	$97.38	8.612%	$105.7664	$105.77	$105.75	$105.80
Purchase #4	$78.65	13.508%	$89.274	$89.27	$89.25	$89.30
Purchase #5	$5.86	7.595%	$6.3051	$6.31	$6.30	$6.30
Purchase #6	$191.26	3.633%	$198.2085	$198.21	$198.20	$198.20
Purchase #7	$63.85	11.637%	$71.2802	$71.28	$71.30	$71.30
7 purchase totals =	$734.57		$790.2590	$790.27	$790.20	$790.30