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	$184.74	11.459%	$205.9094	$205.91	$205.90	$205.90
Purchase #2	$141.46	6.505%	$150.662	$150.66	$150.65	$150.70
Purchase #3	$240.30	4.319%	$250.6786	$250.68	$250.70	$250.70
Purchase #4	$236.57	8.166%	$255.8883	$255.89	$255.90	$255.90
Purchase #5	$104.49	12.454%	$117.5032	$117.50	$117.50	$117.50
Purchase #6	$109.41	9.240%	$119.5195	$119.52	$119.50	$119.50
Purchase #7	$210.94	13.141%	$238.6596	$238.66	$238.65	$238.70
7 purchase totals =	$1,227.91		$1,338.8206	$1,338.82	$1,338.80	$1,338.90