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	$228.33	9.666%	$250.4004	$250.40	$250.40	$250.40
Purchase #2	$133.59	7.370%	$143.4356	$143.44	$143.45	$143.40
Purchase #3	$161.30	13.242%	$182.6593	$182.66	$182.65	$182.70
Purchase #4	$179.73	11.524%	$200.4421	$200.44	$200.45	$200.40
Purchase #5	$62.25	6.289%	$66.1649	$66.16	$66.15	$66.20
Purchase #6	$174.65	12.757%	$196.9301	$196.93	$196.95	$196.90
Purchase #7	$29.96	7.508%	$32.2094	$32.21	$32.20	$32.20
7 purchase totals =	$969.81		$1,072.2418	$1,072.24	$1,072.25	$1,072.20