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	$97.48	3.545%	$100.9357	$100.94	$100.95	$100.90
Purchase #2	$250.34	8.514%	$271.6539	$271.65	$271.65	$271.70
Purchase #3	$83.28	6.799%	$88.9422	$88.94	$88.95	$88.90
Purchase #4	$195.61	3.540%	$202.5346	$202.53	$202.55	$202.50
Purchase #5	$151.87	7.250%	$162.8806	$162.88	$162.90	$162.90
Purchase #6	$80.86	10.159%	$89.0746	$89.07	$89.05	$89.10
Purchase #7	$13.94	13.394%	$15.8071	$15.81	$15.80	$15.80
7 purchase totals =	$873.38		$931.8287	$931.82	$931.85	$931.80