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	$121.79	5.437%	$128.4117	$128.41	$128.40	$128.40
Purchase #2	$241.35	11.709%	$269.6097	$269.61	$269.60	$269.60
Purchase #3	$249.33	7.118%	$267.0773	$267.08	$267.10	$267.10
Purchase #4	$85.83	4.474%	$89.67	$89.67	$89.65	$89.70
Purchase #5	$152.81	3.645%	$158.3799	$158.38	$158.40	$158.40
Purchase #6	$146.54	9.130%	$159.9191	$159.92	$159.90	$159.90
Purchase #7	$93.28	13.548%	$105.9176	$105.92	$105.90	$105.90
7 purchase totals =	$1,090.93		$1,178.9853	$1,178.99	$1,178.95	$1,179.00