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	$90.56	9.791%	$99.4267	$99.43	$99.45	$99.40
Purchase #2	$59.79	11.327%	$66.5624	$66.56	$66.55	$66.60
Purchase #3	$216.27	8.837%	$235.3818	$235.38	$235.40	$235.40
Purchase #4	$210.40	13.856%	$239.553	$239.55	$239.55	$239.60
Purchase #5	$239.46	12.465%	$269.3087	$269.31	$269.30	$269.30
Purchase #6	$144.43	3.172%	$149.0113	$149.01	$149.00	$149.00
Purchase #7	$69.55	4.317%	$72.5525	$72.55	$72.55	$72.60
7 purchase totals =	$1,030.46		$1,131.7964	$1,131.79	$1,131.80	$1,131.90