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	$47.65	7.769%	$51.3519	$51.35	$51.35	$51.40
Purchase #2	$160.32	5.340%	$168.8811	$168.88	$168.90	$168.90
Purchase #3	$42.91	6.685%	$45.7785	$45.78	$45.80	$45.80
Purchase #4	$175.51	9.237%	$191.7219	$191.72	$191.70	$191.70
Purchase #5	$247.92	9.376%	$271.165	$271.17	$271.15	$271.20
Purchase #6	$65.59	6.806%	$70.0541	$70.05	$70.05	$70.10
Purchase #7	$38.83	12.560%	$43.707	$43.71	$43.70	$43.70
7 purchase totals =	$778.73		$842.6595	$842.66	$842.65	$842.80