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	$47.36	6.231%	$50.311	$50.31	$50.30	$50.30
Purchase #2	$154.61	6.799%	$165.1219	$165.12	$165.10	$165.10
Purchase #3	$225.59	5.778%	$238.6246	$238.62	$238.60	$238.60
Purchase #4	$243.39	10.614%	$269.2234	$269.22	$269.20	$269.20
Purchase #5	$89.32	3.527%	$92.4703	$92.47	$92.45	$92.50
Purchase #6	$114.79	4.827%	$120.3309	$120.33	$120.35	$120.30
Purchase #7	$68.70	7.395%	$73.7804	$73.78	$73.80	$73.80
7 purchase totals =	$943.76		$1,009.8625	$1,009.85	$1,009.80	$1,009.80