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	$53.26	6.718%	$56.838	$56.84	$56.85	$56.80
Purchase #2	$84.85	5.247%	$89.3021	$89.30	$89.30	$89.30
Purchase #3	$98.36	5.665%	$103.9321	$103.93	$103.95	$103.90
Purchase #4	$85.36	5.689%	$90.2161	$90.22	$90.20	$90.20
Purchase #5	$119.69	7.392%	$128.5375	$128.54	$128.55	$128.50
Purchase #6	$143.54	13.148%	$162.4126	$162.41	$162.40	$162.40
Purchase #7	$202.95	12.142%	$227.5922	$227.59	$227.60	$227.60
7 purchase totals =	$788.01		$858.8306	$858.83	$858.85	$858.70