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	$51.75	9.483%	$56.6575	$56.66	$56.65	$56.70
Purchase #2	$225.54	13.819%	$256.7074	$256.71	$256.70	$256.70
Purchase #3	$195.36	4.175%	$203.5163	$203.52	$203.50	$203.50
Purchase #4	$250.27	5.798%	$264.7807	$264.78	$264.80	$264.80
Purchase #5	$146.60	6.604%	$156.2815	$156.28	$156.30	$156.30
Purchase #6	$220.62	13.591%	$250.6045	$250.60	$250.60	$250.60
Purchase #7	$125.31	11.168%	$139.3046	$139.30	$139.30	$139.30
7 purchase totals =	$1,215.45		$1,327.8525	$1,327.85	$1,327.85	$1,327.90