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	$77.48	6.568%	$82.5689	$82.57	$82.55	$82.60
Purchase #2	$205.40	11.699%	$229.4297	$229.43	$229.45	$229.40
Purchase #3	$198.33	6.578%	$211.3761	$211.38	$211.40	$211.40
Purchase #4	$100.75	10.532%	$111.361	$111.36	$111.35	$111.40
Purchase #5	$239.79	11.786%	$268.0516	$268.05	$268.05	$268.10
Purchase #6	$79.49	13.485%	$90.2092	$90.21	$90.20	$90.20
Purchase #7	$153.64	6.311%	$163.3362	$163.34	$163.35	$163.30
7 purchase totals =	$1,054.88		$1,156.3327	$1,156.34	$1,156.35	$1,156.40