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	$152.29	6.591%	$162.3274	$162.33	$162.35	$162.30
Purchase #2	$115.65	7.172%	$123.9444	$123.94	$123.95	$123.90
Purchase #3	$209.58	8.560%	$227.52	$227.52	$227.50	$227.50
Purchase #4	$103.57	5.532%	$109.2995	$109.30	$109.30	$109.30
Purchase #5	$64.54	12.320%	$72.4913	$72.49	$72.50	$72.50
Purchase #6	$27.46	12.535%	$30.9021	$30.90	$30.90	$30.90
Purchase #7	$22.90	6.198%	$24.3193	$24.32	$24.30	$24.30
7 purchase totals =	$695.99		$750.8040	$750.80	$750.80	$750.70