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	$221.76	13.120%	$250.8549	$250.85	$250.85	$250.90
Purchase #2	$167.80	6.365%	$178.4805	$178.48	$178.50	$178.50
Purchase #3	$150.99	11.569%	$168.458	$168.46	$168.45	$168.50
Purchase #4	$200.72	3.617%	$207.98	$207.98	$208.00	$208.00
Purchase #5	$183.88	3.383%	$190.1007	$190.10	$190.10	$190.10
Purchase #6	$121.94	6.278%	$129.5954	$129.60	$129.60	$129.60
Purchase #7	$160.69	9.148%	$175.3899	$175.39	$175.40	$175.40
7 purchase totals =	$1,207.78		$1,300.8594	$1,300.86	$1,300.90	$1,301.00