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	$22.27	6.646%	$23.7501	$23.75	$23.75	$23.80
Purchase #2	$178.32	12.198%	$200.0715	$200.07	$200.05	$200.10
Purchase #3	$231.59	7.582%	$249.1492	$249.15	$249.15	$249.10
Purchase #4	$118.76	7.684%	$127.8855	$127.89	$127.90	$127.90
Purchase #5	$67.53	12.398%	$75.9024	$75.90	$75.90	$75.90
Purchase #6	$30.69	7.234%	$32.9101	$32.91	$32.90	$32.90
Purchase #7	$57.27	8.829%	$62.3264	$62.33	$62.35	$62.30
7 purchase totals =	$706.43		$771.9952	$772.00	$772.00	$772.00