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	$38.30	11.859%	$42.842	$42.84	$42.85	$42.80
Purchase #2	$40.35	6.157%	$42.8343	$42.83	$42.85	$42.80
Purchase #3	$195.89	12.483%	$220.3429	$220.34	$220.35	$220.30
Purchase #4	$135.39	4.381%	$141.3214	$141.32	$141.30	$141.30
Purchase #5	$37.71	10.137%	$41.5327	$41.53	$41.55	$41.50
Purchase #6	$190.90	3.447%	$197.4803	$197.48	$197.50	$197.50
Purchase #7	$84.97	6.824%	$90.7684	$90.77	$90.75	$90.80
7 purchase totals =	$723.51		$777.1220	$777.11	$777.15	$777.00