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	$159.53	6.651%	$170.1403	$170.14	$170.15	$170.10
Purchase #2	$80.30	11.220%	$89.3097	$89.31	$89.30	$89.30
Purchase #3	$174.55	12.795%	$196.8837	$196.88	$196.90	$196.90
Purchase #4	$192.73	6.829%	$205.8915	$205.89	$205.90	$205.90
Purchase #5	$109.29	8.856%	$118.9687	$118.97	$118.95	$119.00
Purchase #6	$162.93	13.355%	$184.6893	$184.69	$184.70	$184.70
Purchase #7	$36.71	5.573%	$38.7558	$38.76	$38.75	$38.80
7 purchase totals =	$916.04		$1,004.6390	$1,004.64	$1,004.65	$1,004.70