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	$155.28	5.793%	$164.2754	$164.28	$164.30	$164.30
Purchase #2	$183.90	3.598%	$190.5167	$190.52	$190.50	$190.50
Purchase #3	$220.36	13.816%	$250.8049	$250.80	$250.80	$250.80
Purchase #4	$42.91	6.481%	$45.691	$45.69	$45.70	$45.70
Purchase #5	$88.56	7.141%	$94.8841	$94.88	$94.90	$94.90
Purchase #6	$235.33	11.318%	$261.9646	$261.96	$261.95	$262.00
Purchase #7	$112.74	6.287%	$119.828	$119.83	$119.85	$119.80
7 purchase totals =	$1,039.08		$1,127.9647	$1,127.96	$1,128.00	$1,128.00