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	$78.93	13.506%	$89.5903	$89.59	$89.60	$89.60
Purchase #2	$78.85	13.182%	$89.244	$89.24	$89.25	$89.20
Purchase #3	$201.89	3.115%	$208.1789	$208.18	$208.20	$208.20
Purchase #4	$67.40	6.862%	$72.025	$72.03	$72.05	$72.00
Purchase #5	$147.35	4.584%	$154.1045	$154.10	$154.10	$154.10
Purchase #6	$37.80	6.280%	$40.1738	$40.17	$40.15	$40.20
Purchase #7	$195.46	4.250%	$203.7671	$203.77	$203.75	$203.80
7 purchase totals =	$807.68		$857.0836	$857.08	$857.10	$857.10