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	$112.65	5.243%	$118.5562	$118.56	$118.55	$118.60
Purchase #2	$125.77	7.430%	$135.1147	$135.11	$135.10	$135.10
Purchase #3	$104.54	4.693%	$109.4461	$109.45	$109.45	$109.40
Purchase #4	$106.47	10.243%	$117.3757	$117.38	$117.40	$117.40
Purchase #5	$209.62	4.199%	$218.4219	$218.42	$218.40	$218.40
Purchase #6	$33.41	12.509%	$37.5893	$37.59	$37.60	$37.60
Purchase #7	$97.31	3.275%	$100.4969	$100.50	$100.50	$100.50
7 purchase totals =	$789.77		$837.0008	$837.01	$837.00	$837.00