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	$148.86	7.760%	$160.4115	$160.41	$160.40	$160.40
Purchase #2	$55.79	12.732%	$62.8932	$62.89	$62.90	$62.90
Purchase #3	$217.73	7.148%	$233.2933	$233.29	$233.30	$233.30
Purchase #4	$250.96	3.217%	$259.0334	$259.03	$259.05	$259.00
Purchase #5	$32.51	9.409%	$35.5689	$35.57	$35.55	$35.60
Purchase #6	$115.92	12.151%	$130.0054	$130.01	$130.00	$130.00
Purchase #7	$97.89	4.584%	$102.3773	$102.38	$102.40	$102.40
7 purchase totals =	$919.66		$983.5830	$983.58	$983.60	$983.60