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	$37.56	3.713%	$38.9546	$38.95	$38.95	$39.00
Purchase #2	$150.40	6.329%	$159.9188	$159.92	$159.90	$159.90
Purchase #3	$42.65	4.410%	$44.5309	$44.53	$44.55	$44.50
Purchase #4	$104.87	6.785%	$111.9854	$111.99	$112.00	$112.00
Purchase #5	$216.31	9.837%	$237.5884	$237.59	$237.60	$237.60
Purchase #6	$86.72	5.489%	$91.4801	$91.48	$91.50	$91.50
Purchase #7	$92.85	7.518%	$99.8305	$99.83	$99.85	$99.80
7 purchase totals =	$731.36		$784.2887	$784.29	$784.35	$784.30