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	$16.56	13.434%	$18.7847	$18.78	$18.80	$18.80
Purchase #2	$57.47	12.409%	$64.6015	$64.60	$64.60	$64.60
Purchase #3	$202.31	12.627%	$227.8557	$227.86	$227.85	$227.90
Purchase #4	$247.42	10.695%	$273.8816	$273.88	$273.90	$273.90
Purchase #5	$230.86	9.731%	$253.325	$253.33	$253.35	$253.30
Purchase #6	$155.91	4.275%	$162.5752	$162.58	$162.60	$162.60
Purchase #7	$134.76	9.320%	$147.3196	$147.32	$147.30	$147.30
7 purchase totals =	$1,045.29		$1,148.3433	$1,148.35	$1,148.40	$1,148.40