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	$98.79	11.869%	$110.5154	$110.52	$110.50	$110.50
Purchase #2	$185.40	3.287%	$191.4941	$191.49	$191.50	$191.50
Purchase #3	$77.89	10.579%	$86.13	$86.13	$86.15	$86.10
Purchase #4	$25.86	11.692%	$28.8836	$28.88	$28.90	$28.90
Purchase #5	$6.51	12.704%	$7.337	$7.34	$7.35	$7.30
Purchase #6	$246.59	5.681%	$260.5988	$260.60	$260.60	$260.60
Purchase #7	$7.33	4.201%	$7.6379	$7.64	$7.65	$7.60
7 purchase totals =	$648.37		$692.5968	$692.60	$692.65	$692.50