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	$199.99	6.609%	$213.2073	$213.21	$213.20	$213.20
Purchase #2	$43.48	6.432%	$46.2766	$46.28	$46.30	$46.30
Purchase #3	$150.61	9.321%	$164.6484	$164.65	$164.65	$164.60
Purchase #4	$56.80	4.568%	$59.3946	$59.39	$59.40	$59.40
Purchase #5	$98.78	7.151%	$105.8438	$105.84	$105.85	$105.80
Purchase #6	$201.98	3.599%	$209.2493	$209.25	$209.25	$209.20
Purchase #7	$184.69	10.583%	$204.2357	$204.24	$204.25	$204.20
7 purchase totals =	$936.33		$1,002.8557	$1,002.86	$1,002.90	$1,002.70