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	$107.93	3.652%	$111.8716	$111.87	$111.85	$111.90
Purchase #2	$216.84	4.332%	$226.2335	$226.23	$226.25	$226.20
Purchase #3	$184.53	10.612%	$204.1123	$204.11	$204.10	$204.10
Purchase #4	$119.77	9.681%	$131.3649	$131.36	$131.35	$131.40
Purchase #5	$56.75	5.497%	$59.8695	$59.87	$59.85	$59.90
Purchase #6	$113.63	10.574%	$125.6452	$125.65	$125.65	$125.60
Purchase #7	$18.45	13.132%	$20.8729	$20.87	$20.85	$20.90
7 purchase totals =	$817.90		$879.9699	$879.96	$879.90	$880.00