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	$37.89	4.567%	$39.6204	$39.62	$39.60	$39.60
Purchase #2	$123.45	4.508%	$129.0151	$129.02	$129.00	$129.00
Purchase #3	$234.90	12.731%	$264.8051	$264.81	$264.80	$264.80
Purchase #4	$25.73	10.308%	$28.3822	$28.38	$28.40	$28.40
Purchase #5	$156.89	7.378%	$168.4653	$168.47	$168.45	$168.50
Purchase #6	$75.30	10.181%	$82.9663	$82.97	$82.95	$83.00
Purchase #7	$129.99	4.856%	$136.3023	$136.30	$136.30	$136.30
7 purchase totals =	$784.15		$849.5567	$849.57	$849.50	$849.60