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	$74.48	6.456%	$79.2884	$79.29	$79.30	$79.30
Purchase #2	$125.41	10.505%	$138.5843	$138.58	$138.60	$138.60
Purchase #3	$101.86	7.839%	$109.8448	$109.84	$109.85	$109.80
Purchase #4	$102.54	3.206%	$105.8274	$105.83	$105.85	$105.80
Purchase #5	$80.47	7.627%	$86.6074	$86.61	$86.60	$86.60
Purchase #6	$183.57	7.566%	$197.4589	$197.46	$197.45	$197.50
Purchase #7	$74.53	5.874%	$78.9079	$78.91	$78.90	$78.90
7 purchase totals =	$742.86		$796.5191	$796.52	$796.55	$796.50