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	$119.51	9.841%	$131.271	$131.27	$131.25	$131.30
Purchase #2	$86.38	10.176%	$95.17	$95.17	$95.15	$95.20
Purchase #3	$74.96	10.137%	$82.5587	$82.56	$82.55	$82.60
Purchase #4	$210.93	13.833%	$240.1079	$240.11	$240.10	$240.10
Purchase #5	$148.41	3.378%	$153.4233	$153.42	$153.40	$153.40
Purchase #6	$47.67	13.838%	$54.2666	$54.27	$54.25	$54.30
Purchase #7	$97.53	3.455%	$100.8997	$100.90	$100.90	$100.90
7 purchase totals =	$785.39		$857.6972	$857.70	$857.60	$857.80