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	$81.84	9.193%	$89.3636	$89.36	$89.35	$89.40
Purchase #2	$29.74	5.483%	$31.3706	$31.37	$31.35	$31.40
Purchase #3	$239.43	9.595%	$262.4033	$262.40	$262.40	$262.40
Purchase #4	$64.66	4.205%	$67.379	$67.38	$67.40	$67.40
Purchase #5	$83.48	12.785%	$94.1529	$94.15	$94.15	$94.20
Purchase #6	$182.61	4.786%	$191.3497	$191.35	$191.35	$191.30
Purchase #7	$95.32	7.497%	$102.4661	$102.47	$102.45	$102.50
7 purchase totals =	$777.08		$838.4852	$838.48	$838.45	$838.60