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	$151.78	13.385%	$172.0958	$172.10	$172.10	$172.10
Purchase #2	$64.52	7.315%	$69.2396	$69.24	$69.25	$69.20
Purchase #3	$185.33	6.244%	$196.902	$196.90	$196.90	$196.90
Purchase #4	$116.75	7.484%	$125.4876	$125.49	$125.50	$125.50
Purchase #5	$103.81	11.557%	$115.8073	$115.81	$115.80	$115.80
Purchase #6	$174.75	6.135%	$185.4709	$185.47	$185.45	$185.50
Purchase #7	$205.78	9.299%	$224.9155	$224.92	$224.90	$224.90
7 purchase totals =	$1,002.72		$1,089.9187	$1,089.93	$1,089.90	$1,089.90