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	$166.42	11.436%	$185.4518	$185.45	$185.45	$185.50
Purchase #2	$197.65	12.216%	$221.7949	$221.79	$221.80	$221.80
Purchase #3	$42.38	9.291%	$46.3175	$46.32	$46.30	$46.30
Purchase #4	$79.39	7.629%	$85.4467	$85.45	$85.45	$85.40
Purchase #5	$36.51	13.184%	$41.3235	$41.32	$41.30	$41.30
Purchase #6	$211.96	6.421%	$225.57	$225.57	$225.55	$225.60
Purchase #7	$78.94	10.597%	$87.3053	$87.31	$87.30	$87.30
7 purchase totals =	$813.25		$893.2097	$893.21	$893.15	$893.20