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	$26.29	8.628%	$28.5583	$28.56	$28.55	$28.60
Purchase #2	$225.90	7.809%	$243.5405	$243.54	$243.55	$243.50
Purchase #3	$106.89	6.306%	$113.6305	$113.63	$113.65	$113.60
Purchase #4	$199.79	9.425%	$218.6202	$218.62	$218.60	$218.60
Purchase #5	$78.46	7.107%	$84.0362	$84.04	$84.05	$84.00
Purchase #6	$125.32	11.289%	$139.4674	$139.47	$139.45	$139.50
Purchase #7	$166.35	13.342%	$188.5444	$188.54	$188.55	$188.50
7 purchase totals =	$929.00		$1,016.3975	$1,016.40	$1,016.40	$1,016.30