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	$30.31	8.274%	$32.8178	$32.82	$32.80	$32.80
Purchase #2	$212.81	5.169%	$223.8101	$223.81	$223.80	$223.80
Purchase #3	$121.42	6.534%	$129.3536	$129.35	$129.35	$129.40
Purchase #4	$168.49	6.543%	$179.5143	$179.51	$179.50	$179.50
Purchase #5	$163.28	3.511%	$169.0128	$169.01	$169.00	$169.00
Purchase #6	$186.34	11.772%	$208.2759	$208.28	$208.30	$208.30
Purchase #7	$79.90	12.132%	$89.5935	$89.59	$89.60	$89.60
7 purchase totals =	$962.55		$1,032.3780	$1,032.37	$1,032.35	$1,032.40