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	$218.46	6.709%	$233.1165	$233.12	$233.10	$233.10
Purchase #2	$110.86	7.820%	$119.5293	$119.53	$119.55	$119.50
Purchase #3	$167.54	11.680%	$187.1087	$187.11	$187.10	$187.10
Purchase #4	$137.40	13.177%	$155.5052	$155.51	$155.50	$155.50
Purchase #5	$233.85	4.240%	$243.7652	$243.77	$243.75	$243.80
Purchase #6	$59.66	6.257%	$63.3929	$63.39	$63.40	$63.40
Purchase #7	$72.88	8.788%	$79.2847	$79.28	$79.30	$79.30
7 purchase totals =	$1,000.65		$1,081.7025	$1,081.71	$1,081.70	$1,081.70