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	$79.55	4.538%	$83.16	$83.16	$83.15	$83.20
Purchase #2	$242.41	12.869%	$273.6057	$273.61	$273.60	$273.60
Purchase #3	$78.55	5.358%	$82.7587	$82.76	$82.75	$82.80
Purchase #4	$90.33	6.439%	$96.1463	$96.15	$96.15	$96.10
Purchase #5	$96.87	9.782%	$106.3458	$106.35	$106.35	$106.30
Purchase #6	$128.48	10.161%	$141.5349	$141.53	$141.55	$141.50
Purchase #7	$180.50	6.382%	$192.0195	$192.02	$192.00	$192.00
7 purchase totals =	$896.69		$975.5709	$975.58	$975.55	$975.50