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	$123.37	10.510%	$136.3362	$136.34	$136.35	$136.30
Purchase #2	$80.49	10.736%	$89.1314	$89.13	$89.15	$89.10
Purchase #3	$125.29	9.236%	$136.8618	$136.86	$136.85	$136.90
Purchase #4	$175.30	9.822%	$192.518	$192.52	$192.50	$192.50
Purchase #5	$176.71	4.111%	$183.9745	$183.97	$183.95	$184.00
Purchase #6	$63.84	12.777%	$71.9968	$72.00	$72.00	$72.00
Purchase #7	$135.59	12.130%	$152.0371	$152.04	$152.05	$152.00
7 purchase totals =	$880.59		$962.8558	$962.86	$962.85	$962.80