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	$127.71	6.600%	$136.1389	$136.14	$136.15	$136.10
Purchase #2	$154.45	10.595%	$170.814	$170.81	$170.80	$170.80
Purchase #3	$164.96	12.537%	$185.641	$185.64	$185.65	$185.60
Purchase #4	$51.86	4.586%	$54.2383	$54.24	$54.25	$54.20
Purchase #5	$93.85	6.184%	$99.6537	$99.65	$99.65	$99.70
Purchase #6	$45.56	4.254%	$47.4981	$47.50	$47.50	$47.50
Purchase #7	$91.90	3.496%	$95.1128	$95.11	$95.10	$95.10
7 purchase totals =	$730.29		$789.0968	$789.09	$789.10	$789.00