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	$95.70	4.543%	$100.0477	$100.05	$100.05	$100.00
Purchase #2	$166.36	9.747%	$182.5751	$182.58	$182.60	$182.60
Purchase #3	$185.90	8.801%	$202.2611	$202.26	$202.25	$202.30
Purchase #4	$128.52	8.393%	$139.3067	$139.31	$139.30	$139.30
Purchase #5	$56.60	4.387%	$59.083	$59.08	$59.10	$59.10
Purchase #6	$83.38	9.493%	$91.2953	$91.30	$91.30	$91.30
Purchase #7	$148.94	11.486%	$166.0472	$166.05	$166.05	$166.00
7 purchase totals =	$865.40		$940.6161	$940.63	$940.65	$940.60