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	$125.26	10.855%	$138.857	$138.86	$138.85	$138.90
Purchase #2	$201.43	4.494%	$210.4823	$210.48	$210.50	$210.50
Purchase #3	$65.45	11.365%	$72.8884	$72.89	$72.90	$72.90
Purchase #4	$203.48	9.866%	$223.5553	$223.56	$223.55	$223.60
Purchase #5	$8.37	10.358%	$9.237	$9.24	$9.25	$9.20
Purchase #6	$229.81	3.743%	$238.4118	$238.41	$238.40	$238.40
Purchase #7	$131.91	10.869%	$146.2473	$146.25	$146.25	$146.20
7 purchase totals =	$965.71		$1,039.6791	$1,039.69	$1,039.70	$1,039.70