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	$250.48	8.287%	$271.2373	$271.24	$271.25	$271.20
Purchase #2	$62.57	7.746%	$67.4167	$67.42	$67.40	$67.40
Purchase #3	$81.97	3.155%	$84.5562	$84.56	$84.55	$84.60
Purchase #4	$39.80	7.242%	$42.6823	$42.68	$42.70	$42.70
Purchase #5	$180.71	13.160%	$204.4914	$204.49	$204.50	$204.50
Purchase #6	$101.72	3.369%	$105.1469	$105.15	$105.15	$105.10
Purchase #7	$70.33	12.173%	$78.8913	$78.89	$78.90	$78.90
7 purchase totals =	$787.58		$854.4221	$854.43	$854.45	$854.40