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	$70.33	11.680%	$78.5445	$78.54	$78.55	$78.50
Purchase #2	$138.49	6.225%	$147.111	$147.11	$147.10	$147.10
Purchase #3	$82.58	11.816%	$92.3377	$92.34	$92.35	$92.30
Purchase #4	$237.55	6.746%	$253.5751	$253.58	$253.60	$253.60
Purchase #5	$239.90	6.215%	$254.8098	$254.81	$254.80	$254.80
Purchase #6	$18.46	7.413%	$19.8284	$19.83	$19.85	$19.80
Purchase #7	$211.35	6.147%	$224.3417	$224.34	$224.35	$224.30
7 purchase totals =	$998.66		$1,070.5482	$1,070.55	$1,070.60	$1,070.40