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	$31.40	4.315%	$32.7549	$32.75	$32.75	$32.80
Purchase #2	$247.34	4.107%	$257.4983	$257.50	$257.50	$257.50
Purchase #3	$117.77	8.316%	$127.5638	$127.56	$127.55	$127.60
Purchase #4	$174.84	13.512%	$198.4644	$198.46	$198.45	$198.50
Purchase #5	$52.86	4.749%	$55.3703	$55.37	$55.35	$55.40
Purchase #6	$155.95	8.317%	$168.9204	$168.92	$168.90	$168.90
Purchase #7	$246.25	5.659%	$260.1853	$260.19	$260.20	$260.20
7 purchase totals =	$1,026.41		$1,100.7574	$1,100.75	$1,100.70	$1,100.90