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	$83.41	6.815%	$89.0944	$89.09	$89.10	$89.10
Purchase #2	$227.72	12.818%	$256.9091	$256.91	$256.90	$256.90
Purchase #3	$88.62	7.676%	$95.4225	$95.42	$95.40	$95.40
Purchase #4	$163.33	11.522%	$182.1489	$182.15	$182.15	$182.10
Purchase #5	$114.31	4.721%	$119.7066	$119.71	$119.70	$119.70
Purchase #6	$206.93	7.809%	$223.0892	$223.09	$223.10	$223.10
Purchase #7	$134.34	8.309%	$145.5023	$145.50	$145.50	$145.50
7 purchase totals =	$1,018.66		$1,111.8730	$1,111.87	$1,111.85	$1,111.80