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	$238.35	13.504%	$270.5368	$270.54	$270.55	$270.50
Purchase #2	$175.31	6.643%	$186.9558	$186.96	$186.95	$187.00
Purchase #3	$64.69	10.109%	$71.2295	$71.23	$71.25	$71.20
Purchase #4	$135.92	4.204%	$141.6341	$141.63	$141.65	$141.60
Purchase #5	$186.68	9.636%	$204.6685	$204.67	$204.65	$204.70
Purchase #6	$38.46	11.376%	$42.8352	$42.84	$42.85	$42.80
Purchase #7	$67.53	6.656%	$72.0248	$72.02	$72.00	$72.00
7 purchase totals =	$906.94		$989.8847	$989.89	$989.90	$989.80