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	$173.70	8.451%	$188.3794	$188.38	$188.40	$188.40
Purchase #2	$110.26	11.605%	$123.0557	$123.06	$123.05	$123.10
Purchase #3	$168.66	8.804%	$183.5088	$183.51	$183.50	$183.50
Purchase #4	$119.76	11.666%	$133.7312	$133.73	$133.75	$133.70
Purchase #5	$137.55	9.469%	$150.5746	$150.57	$150.55	$150.60
Purchase #6	$147.52	4.685%	$154.4313	$154.43	$154.45	$154.40
Purchase #7	$80.50	11.779%	$89.9821	$89.98	$90.00	$90.00
7 purchase totals =	$937.95		$1,023.6631	$1,023.66	$1,023.70	$1,023.70