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	$244.34	12.870%	$275.7866	$275.79	$275.80	$275.80
Purchase #2	$92.46	3.115%	$95.3401	$95.34	$95.35	$95.30
Purchase #3	$63.52	11.219%	$70.6463	$70.65	$70.65	$70.60
Purchase #4	$189.60	5.547%	$200.1171	$200.12	$200.10	$200.10
Purchase #5	$116.90	8.455%	$126.7839	$126.78	$126.80	$126.80
Purchase #6	$68.56	5.503%	$72.3329	$72.33	$72.35	$72.30
Purchase #7	$173.39	9.327%	$189.5621	$189.56	$189.55	$189.60
7 purchase totals =	$948.77		$1,030.5690	$1,030.57	$1,030.60	$1,030.50