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	$69.97	12.494%	$78.7121	$78.71	$78.70	$78.70
Purchase #2	$176.76	10.236%	$194.8532	$194.85	$194.85	$194.90
Purchase #3	$227.47	9.449%	$248.9636	$248.96	$248.95	$249.00
Purchase #4	$85.29	10.335%	$94.1047	$94.10	$94.10	$94.10
Purchase #5	$190.43	10.216%	$209.8843	$209.88	$209.90	$209.90
Purchase #6	$82.97	10.730%	$91.8727	$91.87	$91.85	$91.90
Purchase #7	$77.27	13.267%	$87.5214	$87.52	$87.50	$87.50
7 purchase totals =	$910.16		$1,005.9120	$1,005.89	$1,005.85	$1,006.00