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	$170.67	8.116%	$184.5216	$184.52	$184.50	$184.50
Purchase #2	$201.68	12.440%	$226.769	$226.77	$226.75	$226.80
Purchase #3	$132.54	7.517%	$142.503	$142.50	$142.50	$142.50
Purchase #4	$29.93	5.406%	$31.548	$31.55	$31.55	$31.50
Purchase #5	$81.75	10.576%	$90.3959	$90.40	$90.40	$90.40
Purchase #6	$41.77	11.801%	$46.6993	$46.70	$46.70	$46.70
Purchase #7	$243.97	12.276%	$273.9198	$273.92	$273.90	$273.90
7 purchase totals =	$902.31		$996.3566	$996.36	$996.30	$996.30