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	$59.47	7.590%	$63.9838	$63.98	$64.00	$64.00
Purchase #2	$174.83	10.612%	$193.383	$193.38	$193.40	$193.40
Purchase #3	$19.48	6.542%	$20.7544	$20.75	$20.75	$20.80
Purchase #4	$238.61	4.566%	$249.5049	$249.50	$249.50	$249.50
Purchase #5	$191.37	13.192%	$216.6155	$216.62	$216.60	$216.60
Purchase #6	$92.48	7.818%	$99.7101	$99.71	$99.70	$99.70
Purchase #7	$171.82	13.801%	$195.5329	$195.53	$195.55	$195.50
7 purchase totals =	$948.06		$1,039.4846	$1,039.47	$1,039.50	$1,039.50