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	$241.52	11.542%	$269.3962	$269.40	$269.40	$269.40
Purchase #2	$155.60	11.858%	$174.051	$174.05	$174.05	$174.10
Purchase #3	$43.40	3.333%	$44.8465	$44.85	$44.85	$44.80
Purchase #4	$78.64	10.449%	$86.8571	$86.86	$86.85	$86.90
Purchase #5	$77.97	7.438%	$83.7694	$83.77	$83.75	$83.80
Purchase #6	$130.25	10.731%	$144.2271	$144.23	$144.25	$144.20
Purchase #7	$69.31	3.581%	$71.792	$71.79	$71.80	$71.80
7 purchase totals =	$796.69		$874.9393	$874.95	$874.95	$875.00