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	$35.58	11.442%	$39.6511	$39.65	$39.65	$39.70
Purchase #2	$182.42	5.191%	$191.8894	$191.89	$191.90	$191.90
Purchase #3	$48.59	12.303%	$54.568	$54.57	$54.55	$54.60
Purchase #4	$28.51	9.652%	$31.2618	$31.26	$31.25	$31.30
Purchase #5	$128.95	9.484%	$141.1796	$141.18	$141.20	$141.20
Purchase #6	$240.74	7.330%	$258.3862	$258.39	$258.40	$258.40
Purchase #7	$63.49	13.457%	$72.0338	$72.03	$72.05	$72.00
7 purchase totals =	$728.28		$788.9699	$788.97	$789.00	$789.10