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	$9.90	6.758%	$10.569	$10.57	$10.55	$10.60
Purchase #2	$85.66	7.736%	$92.2867	$92.29	$92.30	$92.30
Purchase #3	$130.37	7.259%	$139.8336	$139.83	$139.85	$139.80
Purchase #4	$65.90	8.155%	$71.2741	$71.27	$71.25	$71.30
Purchase #5	$178.77	7.109%	$191.4788	$191.48	$191.50	$191.50
Purchase #6	$46.84	13.315%	$53.0767	$53.08	$53.10	$53.10
Purchase #7	$13.54	11.413%	$15.0853	$15.09	$15.10	$15.10
7 purchase totals =	$530.98		$573.6042	$573.61	$573.65	$573.70