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	$203.49	11.452%	$226.7937	$226.79	$226.80	$226.80
Purchase #2	$81.35	9.542%	$89.1124	$89.11	$89.10	$89.10
Purchase #3	$189.79	11.828%	$212.2384	$212.24	$212.25	$212.20
Purchase #4	$20.54	10.849%	$22.7684	$22.77	$22.75	$22.80
Purchase #5	$116.36	11.591%	$129.8473	$129.85	$129.85	$129.80
Purchase #6	$31.54	3.119%	$32.5237	$32.52	$32.50	$32.50
Purchase #7	$79.81	13.308%	$90.4311	$90.43	$90.45	$90.40
7 purchase totals =	$722.88		$803.7150	$803.71	$803.70	$803.60