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	$27.43	8.389%	$29.7311	$29.73	$29.75	$29.70
Purchase #2	$179.32	9.137%	$195.7045	$195.70	$195.70	$195.70
Purchase #3	$247.48	6.642%	$263.9176	$263.92	$263.90	$263.90
Purchase #4	$126.95	12.146%	$142.3693	$142.37	$142.35	$142.40
Purchase #5	$199.94	11.275%	$222.4832	$222.48	$222.50	$222.50
Purchase #6	$80.74	3.851%	$83.8493	$83.85	$83.85	$83.80
Purchase #7	$215.81	12.362%	$242.4884	$242.49	$242.50	$242.50
7 purchase totals =	$1,077.67		$1,180.5434	$1,180.54	$1,180.55	$1,180.50