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	$37.42	7.648%	$40.2819	$40.28	$40.30	$40.30
Purchase #2	$193.72	3.820%	$201.1201	$201.12	$201.10	$201.10
Purchase #3	$149.82	3.849%	$155.5866	$155.59	$155.60	$155.60
Purchase #4	$85.53	4.445%	$89.3318	$89.33	$89.35	$89.30
Purchase #5	$80.68	10.652%	$89.274	$89.27	$89.25	$89.30
Purchase #6	$210.42	12.344%	$236.3942	$236.39	$236.40	$236.40
Purchase #7	$151.41	7.147%	$162.2313	$162.23	$162.25	$162.20
7 purchase totals =	$909.00		$974.2199	$974.21	$974.25	$974.20