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	$27.57	7.489%	$29.6347	$29.63	$29.65	$29.60
Purchase #2	$19.37	10.765%	$21.4552	$21.46	$21.45	$21.50
Purchase #3	$243.83	12.284%	$273.7821	$273.78	$273.80	$273.80
Purchase #4	$62.65	6.744%	$66.8751	$66.88	$66.90	$66.90
Purchase #5	$127.56	9.620%	$139.8313	$139.83	$139.85	$139.80
Purchase #6	$66.50	7.500%	$71.4875	$71.49	$71.50	$71.50
Purchase #7	$72.76	6.368%	$77.3934	$77.39	$77.40	$77.40
7 purchase totals =	$620.24		$680.4593	$680.46	$680.55	$680.50