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	$128.27	13.853%	$146.0392	$146.04	$146.05	$146.00
Purchase #2	$197.65	9.485%	$216.3971	$216.40	$216.40	$216.40
Purchase #3	$168.59	3.241%	$174.054	$174.05	$174.05	$174.10
Purchase #4	$61.50	9.582%	$67.3929	$67.39	$67.40	$67.40
Purchase #5	$60.86	11.394%	$67.7944	$67.79	$67.80	$67.80
Purchase #6	$48.71	13.593%	$55.3312	$55.33	$55.35	$55.30
Purchase #7	$237.95	5.850%	$251.8701	$251.87	$251.85	$251.90
7 purchase totals =	$903.53		$978.8789	$978.87	$978.90	$978.90