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	$231.73	11.524%	$258.4346	$258.43	$258.45	$258.40
Purchase #2	$31.35	13.594%	$35.6117	$35.61	$35.60	$35.60
Purchase #3	$85.39	7.396%	$91.7054	$91.71	$91.70	$91.70
Purchase #4	$23.33	8.852%	$25.3952	$25.40	$25.40	$25.40
Purchase #5	$102.58	4.134%	$106.8207	$106.82	$106.80	$106.80
Purchase #6	$99.59	5.755%	$105.3214	$105.32	$105.30	$105.30
Purchase #7	$104.61	8.343%	$113.3376	$113.34	$113.35	$113.30
7 purchase totals =	$678.58		$736.6266	$736.63	$736.60	$736.50