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	$41.35	13.429%	$46.9029	$46.90	$46.90	$46.90
Purchase #2	$242.77	11.506%	$270.7031	$270.70	$270.70	$270.70
Purchase #3	$106.53	7.579%	$114.6039	$114.60	$114.60	$114.60
Purchase #4	$79.60	3.112%	$82.0772	$82.08	$82.10	$82.10
Purchase #5	$195.61	6.613%	$208.5457	$208.55	$208.55	$208.50
Purchase #6	$85.31	5.221%	$89.764	$89.76	$89.75	$89.80
Purchase #7	$104.83	4.493%	$109.54	$109.54	$109.55	$109.50
7 purchase totals =	$856.00		$922.1368	$922.13	$922.15	$922.10