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	$156.70	6.818%	$167.3838	$167.38	$167.40	$167.40
Purchase #2	$179.56	4.634%	$187.8808	$187.88	$187.90	$187.90
Purchase #3	$140.73	4.377%	$146.8898	$146.89	$146.90	$146.90
Purchase #4	$101.68	4.364%	$106.1173	$106.12	$106.10	$106.10
Purchase #5	$114.29	6.312%	$121.504	$121.50	$121.50	$121.50
Purchase #6	$87.62	3.791%	$90.9417	$90.94	$90.95	$90.90
Purchase #7	$31.56	12.404%	$35.4747	$35.47	$35.45	$35.50
7 purchase totals =	$812.14		$856.1921	$856.18	$856.20	$856.20