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	$111.68	8.224%	$120.8646	$120.86	$120.85	$120.90
Purchase #2	$74.35	7.352%	$79.8162	$79.82	$79.80	$79.80
Purchase #3	$57.43	3.141%	$59.2339	$59.23	$59.25	$59.20
Purchase #4	$82.86	3.436%	$85.7071	$85.71	$85.70	$85.70
Purchase #5	$167.76	3.566%	$173.7423	$173.74	$173.75	$173.70
Purchase #6	$152.33	11.798%	$170.3019	$170.30	$170.30	$170.30
Purchase #7	$176.98	13.151%	$200.2546	$200.25	$200.25	$200.30
7 purchase totals =	$823.39		$889.9206	$889.91	$889.90	$889.90