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	$140.30	4.689%	$146.8787	$146.88	$146.90	$146.90
Purchase #2	$83.32	8.357%	$90.2831	$90.28	$90.30	$90.30
Purchase #3	$161.50	3.598%	$167.3108	$167.31	$167.30	$167.30
Purchase #4	$13.88	5.392%	$14.6284	$14.63	$14.65	$14.60
Purchase #5	$126.48	6.375%	$134.5431	$134.54	$134.55	$134.50
Purchase #6	$45.83	6.473%	$48.7966	$48.80	$48.80	$48.80
Purchase #7	$196.41	7.393%	$210.9306	$210.93	$210.95	$210.90
7 purchase totals =	$767.72		$813.3713	$813.37	$813.45	$813.30