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	$140.30	8.424%	$152.1189	$152.12	$152.10	$152.10
Purchase #2	$112.85	13.577%	$128.1716	$128.17	$128.15	$128.20
Purchase #3	$147.73	13.404%	$167.5317	$167.53	$167.55	$167.50
Purchase #4	$122.87	11.193%	$136.6228	$136.62	$136.60	$136.60
Purchase #5	$198.55	13.350%	$225.0564	$225.06	$225.05	$225.10
Purchase #6	$138.35	3.294%	$142.9072	$142.91	$142.90	$142.90
Purchase #7	$81.64	9.469%	$89.3705	$89.37	$89.35	$89.40
7 purchase totals =	$942.29		$1,041.7791	$1,041.78	$1,041.70	$1,041.80