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	$85.90	3.456%	$88.8687	$88.87	$88.85	$88.90
Purchase #2	$249.65	13.740%	$283.9519	$283.95	$283.95	$284.00
Purchase #3	$209.31	4.304%	$218.3187	$218.32	$218.30	$218.30
Purchase #4	$72.94	13.604%	$82.8628	$82.86	$82.85	$82.90
Purchase #5	$210.29	3.844%	$218.3735	$218.37	$218.35	$218.40
Purchase #6	$28.56	12.314%	$32.0769	$32.08	$32.10	$32.10
Purchase #7	$140.40	6.565%	$149.6173	$149.62	$149.60	$149.60
7 purchase totals =	$997.05		$1,074.0698	$1,074.07	$1,074.00	$1,074.20