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	$29.56	5.788%	$31.2709	$31.27	$31.25	$31.30
Purchase #2	$7.61	3.115%	$7.8471	$7.85	$7.85	$7.80
Purchase #3	$119.33	12.562%	$134.3202	$134.32	$134.30	$134.30
Purchase #4	$30.59	3.164%	$31.5579	$31.56	$31.55	$31.60
Purchase #5	$140.58	4.524%	$146.9398	$146.94	$146.95	$146.90
Purchase #6	$176.42	8.787%	$191.922	$191.92	$191.90	$191.90
Purchase #7	$18.29	7.606%	$19.6811	$19.68	$19.70	$19.70
7 purchase totals =	$522.38		$563.5390	$563.54	$563.50	$563.50