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	$86.72	3.586%	$89.8298	$89.83	$89.85	$89.80
Purchase #2	$223.96	6.668%	$238.8937	$238.89	$238.90	$238.90
Purchase #3	$79.79	11.263%	$88.7767	$88.78	$88.80	$88.80
Purchase #4	$29.53	8.828%	$32.1369	$32.14	$32.15	$32.10
Purchase #5	$109.53	3.644%	$113.5213	$113.52	$113.50	$113.50
Purchase #6	$62.90	8.436%	$68.2062	$68.21	$68.20	$68.20
Purchase #7	$163.57	6.424%	$174.0777	$174.08	$174.10	$174.10
7 purchase totals =	$756.00		$805.4423	$805.45	$805.50	$805.40