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	$85.38	4.732%	$89.4202	$89.42	$89.40	$89.40
Purchase #2	$24.56	11.283%	$27.3311	$27.33	$27.35	$27.30
Purchase #3	$207.78	9.228%	$226.9539	$226.95	$226.95	$227.00
Purchase #4	$32.43	5.687%	$34.2743	$34.27	$34.25	$34.30
Purchase #5	$192.55	4.164%	$200.5678	$200.57	$200.55	$200.60
Purchase #6	$218.85	11.352%	$243.6939	$243.69	$243.70	$243.70
Purchase #7	$67.97	10.510%	$75.1136	$75.11	$75.10	$75.10
7 purchase totals =	$829.52		$897.3548	$897.34	$897.30	$897.40