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	$245.69	9.623%	$269.3327	$269.33	$269.35	$269.30
Purchase #2	$79.41	12.354%	$89.2203	$89.22	$89.20	$89.20
Purchase #3	$221.61	9.556%	$242.7871	$242.79	$242.80	$242.80
Purchase #4	$56.46	6.691%	$60.2377	$60.24	$60.25	$60.20
Purchase #5	$26.99	3.627%	$27.9689	$27.97	$27.95	$28.00
Purchase #6	$80.54	10.511%	$89.0056	$89.01	$89.00	$89.00
Purchase #7	$31.45	10.853%	$34.8633	$34.86	$34.85	$34.90
7 purchase totals =	$742.15		$813.4156	$813.42	$813.40	$813.40