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	$9.99	5.602%	$10.5496	$10.55	$10.55	$10.50
Purchase #2	$155.44	13.639%	$176.6405	$176.64	$176.65	$176.60
Purchase #3	$55.53	7.344%	$59.6081	$59.61	$59.60	$59.60
Purchase #4	$86.72	11.410%	$96.6148	$96.61	$96.60	$96.60
Purchase #5	$65.72	11.690%	$73.4027	$73.40	$73.40	$73.40
Purchase #6	$226.97	7.423%	$243.818	$243.82	$243.80	$243.80
Purchase #7	$172.36	8.773%	$187.4811	$187.48	$187.50	$187.50
7 purchase totals =	$772.73		$848.1148	$848.11	$848.10	$848.00