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	$138.69	6.389%	$147.5509	$147.55	$147.55	$147.60
Purchase #2	$147.41	6.670%	$157.2422	$157.24	$157.25	$157.20
Purchase #3	$93.92	13.851%	$106.9289	$106.93	$106.95	$106.90
Purchase #4	$178.51	3.700%	$185.1149	$185.11	$185.10	$185.10
Purchase #5	$80.79	6.581%	$86.1068	$86.11	$86.10	$86.10
Purchase #6	$90.31	10.277%	$99.5912	$99.59	$99.60	$99.60
Purchase #7	$92.54	13.761%	$105.2744	$105.27	$105.25	$105.30
7 purchase totals =	$822.17		$887.8093	$887.80	$887.80	$887.80