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	$28.39	7.245%	$30.4469	$30.45	$30.45	$30.40
Purchase #2	$210.50	4.847%	$220.7029	$220.70	$220.70	$220.70
Purchase #3	$179.61	9.438%	$196.5616	$196.56	$196.55	$196.60
Purchase #4	$60.76	4.352%	$63.4043	$63.40	$63.40	$63.40
Purchase #5	$143.41	7.616%	$154.3321	$154.33	$154.35	$154.30
Purchase #6	$137.98	11.179%	$153.4048	$153.40	$153.40	$153.40
Purchase #7	$112.82	9.600%	$123.6507	$123.65	$123.65	$123.70
7 purchase totals =	$873.47		$942.5033	$942.49	$942.50	$942.50