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	$112.48	11.484%	$125.3972	$125.40	$125.40	$125.40
Purchase #2	$152.95	10.253%	$168.632	$168.63	$168.65	$168.60
Purchase #3	$44.65	13.296%	$50.5867	$50.59	$50.60	$50.60
Purchase #4	$41.91	9.484%	$45.8847	$45.88	$45.90	$45.90
Purchase #5	$138.61	9.239%	$151.4162	$151.42	$151.40	$151.40
Purchase #6	$42.64	10.391%	$47.0707	$47.07	$47.05	$47.10
Purchase #7	$180.98	8.697%	$196.7198	$196.72	$196.70	$196.70
7 purchase totals =	$714.22		$785.7073	$785.71	$785.70	$785.70