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	$39.74	8.414%	$43.0837	$43.08	$43.10	$43.10
Purchase #2	$248.65	6.469%	$264.7352	$264.74	$264.75	$264.70
Purchase #3	$31.37	3.723%	$32.5379	$32.54	$32.55	$32.50
Purchase #4	$244.94	7.598%	$263.5505	$263.55	$263.55	$263.60
Purchase #5	$79.59	5.261%	$83.7772	$83.78	$83.80	$83.80
Purchase #6	$108.90	3.197%	$112.3815	$112.38	$112.40	$112.40
Purchase #7	$40.42	12.531%	$45.485	$45.49	$45.50	$45.50
7 purchase totals =	$793.61		$845.5510	$845.56	$845.65	$845.60