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	$246.56	9.831%	$270.7993	$270.80	$270.80	$270.80
Purchase #2	$105.54	13.468%	$119.7541	$119.75	$119.75	$119.80
Purchase #3	$60.67	3.274%	$62.6563	$62.66	$62.65	$62.70
Purchase #4	$129.49	4.215%	$134.948	$134.95	$134.95	$134.90
Purchase #5	$144.95	9.268%	$158.384	$158.38	$158.40	$158.40
Purchase #6	$185.86	12.168%	$208.4754	$208.48	$208.50	$208.50
Purchase #7	$62.89	13.400%	$71.3173	$71.32	$71.30	$71.30
7 purchase totals =	$935.96		$1,026.3344	$1,026.34	$1,026.35	$1,026.40