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	$45.75	9.118%	$49.9215	$49.92	$49.90	$49.90
Purchase #2	$31.84	3.358%	$32.9092	$32.91	$32.90	$32.90
Purchase #3	$164.61	13.780%	$187.2933	$187.29	$187.30	$187.30
Purchase #4	$152.30	11.638%	$170.0247	$170.02	$170.00	$170.00
Purchase #5	$167.87	12.864%	$189.4648	$189.46	$189.45	$189.50
Purchase #6	$53.33	4.411%	$55.6824	$55.68	$55.70	$55.70
Purchase #7	$169.32	12.534%	$190.5426	$190.54	$190.55	$190.50
7 purchase totals =	$785.02		$875.8385	$875.82	$875.80	$875.80