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	$55.83	6.673%	$59.5555	$59.56	$59.55	$59.60
Purchase #2	$84.27	11.163%	$93.6771	$93.68	$93.70	$93.70
Purchase #3	$166.56	12.175%	$186.8387	$186.84	$186.85	$186.80
Purchase #4	$25.40	11.158%	$28.2341	$28.23	$28.25	$28.20
Purchase #5	$236.57	5.209%	$248.8929	$248.89	$248.90	$248.90
Purchase #6	$97.89	7.606%	$105.3355	$105.34	$105.35	$105.30
Purchase #7	$5.79	4.183%	$6.0322	$6.03	$6.05	$6.00
7 purchase totals =	$672.31		$728.5660	$728.57	$728.65	$728.50