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	$165.64	11.867%	$185.2965	$185.30	$185.30	$185.30
Purchase #2	$50.32	12.156%	$56.4369	$56.44	$56.45	$56.40
Purchase #3	$186.82	12.154%	$209.5261	$209.53	$209.55	$209.50
Purchase #4	$49.73	13.751%	$56.5684	$56.57	$56.55	$56.60
Purchase #5	$227.45	12.308%	$255.4445	$255.44	$255.45	$255.40
Purchase #6	$209.75	3.417%	$216.9172	$216.92	$216.90	$216.90
Purchase #7	$132.70	6.421%	$141.2207	$141.22	$141.20	$141.20
7 purchase totals =	$1,022.41		$1,121.4103	$1,121.42	$1,121.40	$1,121.30