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	$29.81	6.702%	$31.8079	$31.81	$31.80	$31.80
Purchase #2	$93.47	5.314%	$98.437	$98.44	$98.45	$98.40
Purchase #3	$218.62	4.747%	$228.9979	$229.00	$229.00	$229.00
Purchase #4	$57.32	8.613%	$62.257	$62.26	$62.25	$62.30
Purchase #5	$84.40	6.387%	$89.7906	$89.79	$89.80	$89.80
Purchase #6	$29.60	6.549%	$31.5385	$31.54	$31.55	$31.50
Purchase #7	$147.40	6.142%	$156.4533	$156.45	$156.45	$156.50
7 purchase totals =	$660.62		$699.2822	$699.29	$699.30	$699.30