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	$155.90	8.300%	$168.8397	$168.84	$168.85	$168.80
Purchase #2	$175.66	11.794%	$196.3773	$196.38	$196.40	$196.40
Purchase #3	$122.81	3.663%	$127.3085	$127.31	$127.30	$127.30
Purchase #4	$240.44	13.765%	$273.5366	$273.54	$273.55	$273.50
Purchase #5	$74.96	11.169%	$83.3323	$83.33	$83.35	$83.30
Purchase #6	$142.27	11.541%	$158.6894	$158.69	$158.70	$158.70
Purchase #7	$216.70	4.129%	$225.6475	$225.65	$225.65	$225.60
7 purchase totals =	$1,128.74		$1,233.7313	$1,233.74	$1,233.80	$1,233.60