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	$242.60	8.579%	$263.4127	$263.41	$263.40	$263.40
Purchase #2	$186.42	13.340%	$211.2884	$211.29	$211.30	$211.30
Purchase #3	$245.61	4.840%	$257.4975	$257.50	$257.50	$257.50
Purchase #4	$40.52	12.204%	$45.4651	$45.47	$45.45	$45.50
Purchase #5	$124.80	13.675%	$141.8664	$141.87	$141.85	$141.90
Purchase #6	$131.61	5.836%	$139.2908	$139.29	$139.30	$139.30
Purchase #7	$57.56	12.113%	$64.5322	$64.53	$64.55	$64.50
7 purchase totals =	$1,029.12		$1,123.3531	$1,123.36	$1,123.35	$1,123.40