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	$32.89	11.228%	$36.5829	$36.58	$36.60	$36.60
Purchase #2	$176.60	9.364%	$193.1368	$193.14	$193.15	$193.10
Purchase #3	$189.72	11.365%	$211.2817	$211.28	$211.30	$211.30
Purchase #4	$63.90	12.873%	$72.1258	$72.13	$72.15	$72.10
Purchase #5	$221.46	12.540%	$249.2311	$249.23	$249.25	$249.20
Purchase #6	$201.74	6.682%	$215.2203	$215.22	$215.20	$215.20
Purchase #7	$93.52	11.554%	$104.3253	$104.33	$104.35	$104.30
7 purchase totals =	$979.83		$1,081.9039	$1,081.91	$1,082.00	$1,081.80