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	$40.63	12.828%	$45.842	$45.84	$45.85	$45.80
Purchase #2	$38.58	9.805%	$42.3628	$42.36	$42.35	$42.40
Purchase #3	$50.72	4.807%	$53.1581	$53.16	$53.15	$53.20
Purchase #4	$221.66	10.797%	$245.5926	$245.59	$245.60	$245.60
Purchase #5	$177.98	10.561%	$196.7765	$196.78	$196.80	$196.80
Purchase #6	$42.53	4.591%	$44.4826	$44.48	$44.50	$44.50
Purchase #7	$146.53	11.815%	$163.8425	$163.84	$163.85	$163.80
7 purchase totals =	$718.63		$792.0571	$792.05	$792.10	$792.10