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	$230.41	12.391%	$258.9601	$258.96	$258.95	$259.00
Purchase #2	$150.89	3.698%	$156.4699	$156.47	$156.45	$156.50
Purchase #3	$140.64	3.179%	$145.1109	$145.11	$145.10	$145.10
Purchase #4	$114.46	7.627%	$123.1899	$123.19	$123.20	$123.20
Purchase #5	$125.91	11.313%	$140.1542	$140.15	$140.15	$140.20
Purchase #6	$53.98	8.415%	$58.5224	$58.52	$58.50	$58.50
Purchase #7	$196.80	8.630%	$213.7838	$213.78	$213.80	$213.80
7 purchase totals =	$1,013.09		$1,096.1912	$1,096.18	$1,096.15	$1,096.30