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	$52.87	12.609%	$59.5364	$59.54	$59.55	$59.50
Purchase #2	$162.68	13.741%	$185.0339	$185.03	$185.05	$185.00
Purchase #3	$87.94	11.744%	$98.2677	$98.27	$98.25	$98.30
Purchase #4	$48.76	4.187%	$50.8016	$50.80	$50.80	$50.80
Purchase #5	$135.51	9.232%	$148.0203	$148.02	$148.00	$148.00
Purchase #6	$185.30	8.134%	$200.3723	$200.37	$200.35	$200.40
Purchase #7	$148.27	5.812%	$156.8875	$156.89	$156.90	$156.90
7 purchase totals =	$821.33		$898.9197	$898.92	$898.90	$898.90