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	$181.90	10.216%	$200.4829	$200.48	$200.50	$200.50
Purchase #2	$113.85	9.556%	$124.7295	$124.73	$124.75	$124.70
Purchase #3	$129.77	13.584%	$147.398	$147.40	$147.40	$147.40
Purchase #4	$234.81	7.271%	$251.883	$251.88	$251.90	$251.90
Purchase #5	$211.68	12.781%	$238.7348	$238.73	$238.75	$238.70
Purchase #6	$53.53	10.270%	$59.0275	$59.03	$59.05	$59.00
Purchase #7	$111.93	4.444%	$116.9042	$116.90	$116.90	$116.90
7 purchase totals =	$1,037.47		$1,139.1599	$1,139.15	$1,139.25	$1,139.10