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	$36.87	4.406%	$38.4945	$38.49	$38.50	$38.50
Purchase #2	$198.94	6.398%	$211.6682	$211.67	$211.65	$211.70
Purchase #3	$220.36	13.663%	$250.4678	$250.47	$250.45	$250.50
Purchase #4	$72.36	9.115%	$78.9556	$78.96	$78.95	$79.00
Purchase #5	$175.61	12.443%	$197.4612	$197.46	$197.45	$197.50
Purchase #6	$139.55	6.368%	$148.4365	$148.44	$148.45	$148.40
Purchase #7	$49.47	7.653%	$53.2559	$53.26	$53.25	$53.30
7 purchase totals =	$893.16		$978.7397	$978.75	$978.70	$978.90