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	$29.97	10.604%	$33.148	$33.15	$33.15	$33.10
Purchase #2	$48.64	12.756%	$54.8445	$54.84	$54.85	$54.80
Purchase #3	$180.98	10.237%	$199.5069	$199.51	$199.50	$199.50
Purchase #4	$57.86	3.298%	$59.7682	$59.77	$59.75	$59.80
Purchase #5	$37.78	11.390%	$42.0831	$42.08	$42.10	$42.10
Purchase #6	$55.45	5.252%	$58.3622	$58.36	$58.35	$58.40
Purchase #7	$39.90	8.320%	$43.2197	$43.22	$43.20	$43.20
7 purchase totals =	$450.58		$490.9326	$490.93	$490.90	$490.90