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	$67.27	12.235%	$75.5005	$75.50	$75.50	$75.50
Purchase #2	$79.66	6.824%	$85.096	$85.10	$85.10	$85.10
Purchase #3	$56.63	5.808%	$59.9191	$59.92	$59.90	$59.90
Purchase #4	$203.68	8.769%	$221.5407	$221.54	$221.55	$221.50
Purchase #5	$226.31	9.700%	$248.2621	$248.26	$248.25	$248.30
Purchase #6	$35.78	10.311%	$39.4693	$39.47	$39.45	$39.50
Purchase #7	$84.75	12.216%	$95.1031	$95.10	$95.10	$95.10
7 purchase totals =	$754.08		$824.8908	$824.89	$824.85	$824.90