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	$31.27	10.188%	$34.4558	$34.46	$34.45	$34.50
Purchase #2	$181.96	9.520%	$199.2826	$199.28	$199.30	$199.30
Purchase #3	$86.39	3.791%	$89.665	$89.67	$89.65	$89.70
Purchase #4	$108.38	11.308%	$120.6356	$120.64	$120.65	$120.60
Purchase #5	$208.67	9.496%	$228.4853	$228.49	$228.50	$228.50
Purchase #6	$85.56	9.246%	$93.4709	$93.47	$93.45	$93.50
Purchase #7	$216.44	9.103%	$236.1425	$236.14	$236.15	$236.10
7 purchase totals =	$918.67		$1,002.1377	$1,002.15	$1,002.15	$1,002.20