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	$247.64	9.123%	$270.2322	$270.23	$270.25	$270.20
Purchase #2	$79.62	9.446%	$87.1409	$87.14	$87.15	$87.10
Purchase #3	$163.56	4.850%	$171.4927	$171.49	$171.50	$171.50
Purchase #4	$82.66	5.107%	$86.8814	$86.88	$86.90	$86.90
Purchase #5	$135.69	9.661%	$148.799	$148.80	$148.80	$148.80
Purchase #6	$111.59	10.484%	$123.2891	$123.29	$123.30	$123.30
Purchase #7	$48.85	11.456%	$54.4463	$54.45	$54.45	$54.40
7 purchase totals =	$869.61		$942.2816	$942.28	$942.35	$942.20