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	$56.58	5.871%	$59.9018	$59.90	$59.90	$59.90
Purchase #2	$104.84	9.271%	$114.5597	$114.56	$114.55	$114.60
Purchase #3	$16.40	8.192%	$17.7435	$17.74	$17.75	$17.70
Purchase #4	$228.98	5.843%	$242.3593	$242.36	$242.35	$242.40
Purchase #5	$88.68	13.252%	$100.4319	$100.43	$100.45	$100.40
Purchase #6	$222.48	6.802%	$237.6131	$237.61	$237.60	$237.60
Purchase #7	$63.50	12.311%	$71.3175	$71.32	$71.30	$71.30
7 purchase totals =	$781.46		$843.9268	$843.92	$843.90	$843.90