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	$185.89	12.222%	$208.6095	$208.61	$208.60	$208.60
Purchase #2	$36.91	9.172%	$40.2954	$40.30	$40.30	$40.30
Purchase #3	$64.85	12.160%	$72.7358	$72.74	$72.75	$72.70
Purchase #4	$228.73	13.369%	$259.3089	$259.31	$259.30	$259.30
Purchase #5	$84.38	13.344%	$95.6397	$95.64	$95.65	$95.60
Purchase #6	$99.70	5.120%	$104.8046	$104.80	$104.80	$104.80
Purchase #7	$198.45	8.358%	$215.0365	$215.04	$215.05	$215.00
7 purchase totals =	$898.91		$996.4304	$996.44	$996.45	$996.30