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	$52.79	12.188%	$59.224	$59.22	$59.20	$59.20
Purchase #2	$206.43	3.217%	$213.0709	$213.07	$213.05	$213.10
Purchase #3	$96.47	11.669%	$107.7271	$107.73	$107.75	$107.70
Purchase #4	$197.72	11.579%	$220.614	$220.61	$220.60	$220.60
Purchase #5	$222.31	7.210%	$238.3386	$238.34	$238.35	$238.30
Purchase #6	$55.67	10.253%	$61.3778	$61.38	$61.40	$61.40
Purchase #7	$72.79	8.389%	$78.8964	$78.90	$78.90	$78.90
7 purchase totals =	$904.18		$979.2488	$979.25	$979.25	$979.20